Portside

First, he said, came the threat to break his legs. Next came the telephoned death threats.

When that did not stop Mark Rosenthal from running for the presidency of his union local, his opponents threw him off the ballot in what his supporters insist was a kangaroo proceeding.

That was three years ago, and this happened not in the notoriously corrupt teamsters' or longshoremen's unions, but in District Council 37, the umbrella group representing New York City workers, which was long considered a beacon of progressive unionism but is now the target of many corruption investigations.

This summer, Mr. Rosenthal got his revenge. He won the presidency of his local in a landslide, and he has quickly become the go-to guy for hundreds of would-be reformers eager to end what they see as widespread embezzlement and election fraud in District Council 37 of the American Federation of State, County and Municipal Employees.

Mr. Rosenthal, whose 2,400-member local, Motor Vehicle Operators Local 983, represents drivers and boiler tenders, seems an unlikely repository for such hopes. Just three months ago, he was an obscure truck driver in the city's Parks Department. He is an admittedly overweight 46-year-old with a foghorn voice who some other union leaders say is abrasive and publicity hungry.

But what Mr. Rosenthal may lack in polish and experience, he more than makes up for with street smarts, persistence and courage. He knows the threats against him might have some real muscle behind them -- he has repeatedly heard how a previous president of his local, Frank Morelli, was beaten in what is now Mr. Rosenthal's office because he refused to make payments to organized crime figures.

''I'm not going to lie that I'm not fearful,'' Mr. Rosenthal said. ''My whole executive board, they're all afraid for my safety.''

Despite such fears, Mr. Rosenthal has become the most outspoken critic of District Council 37, which represents 120,000 New York City municipal employees, including secretaries, social workers and engineers.

Stanley Hill, the district council's executive director, acknowledges that the Manhattan District Attorney has subpoenaed documents from 12 of the council's 56 locals as part of a wide-ranging investigation into allegations of embezzlement, falsification of records and kickbacks from caterers, lawyers and other contractors, as well as having the union pay for trips overseas and personal credit card bills. Several union officials say the District Attorney's office has told them to expect a wave of indictments this fall.

''This place is a cesspool of corruption,'' Mr. Rosenthal said. ''I was really shocked that this could happen in our union because our union has always had an honorable reputation.''

Since taking the helm of Local 983 in July, Mr. Rosenthal has not wasted any time in shaking things up.

He persuaded his local's executive board to expel his predecessor, Robert Taylor, from the union and order him to pay back $400,000 because he had run up extraordinary expenses without receiving approval at membership meetings, as is required by the local's constitution. According to documents provided by Mr. Rosenthal, those expenses included $45,000 for refreshments for four membership meetings in 1995, $91,000 for the 1995 Christmas party and $81,990 for the 1993 Christmas party.

Mr. Taylor's phone number was not listed, and officials at District Council 37 said they were unable to reach him for comment.

Mr. Rosenthal has also sought to cancel a $450,000 contract (he called the amount outrageous) that his predecessor awarded, in advance, to a lawyer, Adam Ira Klein, to handle a salary arbitration for the 250 boiler tenders in his local. He estimates that Mr. Klein has averaged more than $3,000 an hour for the work put in so far. Mr. Klein did not respond to repeated phone calls.

$1,200 Monthly Check

For No Known Work

In addition, Mr. Rosenthal has stopped his predecessor's practice of sending a $1,200 check each month to Negotiations Consulting, a Long Island company run by Gerard Di Nardo, the son of Thomas DiNardo, who headed the boiler tenders' local before he merged it with Local 983. Mr. Rosenthal's lawyer, Arthur Schwartz, said he could find no evidence that Negotiations Consulting, of Deer Park, had done any work for the union. Gerard DiNardo did not return repeated phone calls.

Shortly after being elected, Mr. Rosenthal, a Baruch College dropout who worked for the Parks Department for 27 years, became one of the founders of the Committee for Real Change in D.C. 37, a group of dissidents that is pressing for more oversight of each local's finances and elections.

Mr. Rosenthal has ruffled lots of feathers in his two months running Local 983, whose members include City Hall chauffeurs, tow truck operators and milk drivers for the city's schools. He has had ambivalent words about Mr. Hill, even though he has often consulted the district council's leader for advice on running Local 983. He praises Mr. Hill for his hard work and dedication to the members, but he occasionally attacks him for siding with unsavory incumbents.

Mr. Hill faulted Mr. Rosenthal for seeming more eager to run to the news media to make his complaints than to work with the district council's leadership to solve them. Some other union leaders had harsher words, calling Mr. Rosenthal undiplomatic and too confrontational. And Mr. Taylor's backers attack Mr. Rosenthal as inexperienced and incompetent, saying that just a few weeks ago he was a nobody helping to pick up papers in the parks.

When a few longtime union leaders crashed a meeting of the Committee for Real Change two weeks ago, James Tucciarelli, president of the sewage treatment workers local, who was one of the crashers, grew so enraged with Mr. Rosenthal that he nearly attacked him.

According to union members who attended themeeting, Mr. Rosenthal angered Mr. Tucciarelli by telling the longtime leaders: ''If you don't reform, you're going to be gone. You won't be here in three years.'' Mr. Tucciarelli said he took that as a personal threat, but Mr. Rosenthal insisted that he was merely warning that veteran leaders would be voted out if they did not embrace change.

Mr. Rosenthal remembers well the two incidents that persuaded him to run for the presidency. In late 1994, he went to a union meeting to tell the leadership of his local that he and other parks workers feared they would lose their jobs as the Giuliani administration placed more and more workfare workers in the parks.

''Their response was, 'You're lucky you have a job,' '' Mr. Rosenthal recalled. ''I was really upset with them. I told the guys in the garage: 'These guys don't want to listen. We should run a candidate against Bob Taylor.' My local is predominantly black and Hispanic, and I didn't think I had a good chance to win because I was white. I was actively looking for a candidate. The guys turned around and said, 'Mark, why don't you run?' ''

'Break Your Legs

And Have You Fired'

So Mr. Rosenthal, who had a reputation as a loud advocate for aggrieved co-workers, began thinking of running. At the union's 1994 Christmas party, he recalled, he was having a meal when a high-ranking official of the local approached him and said: ''We hear you're thinking of running. Don't do it. We're from Bensonhurst. We can always break your legs and have you fired.'' Later, Mr. Rosenthal added, the official said he was just kidding. ''But he wasn't kidding. It was definitely a matter of intimidation.''

A tough, burly blue-collar worker who has lived in the Pelham Parkway section of the Bronx all his life, Mr. Rosenthal was not about to be intimidated. He grew so angry, he said, that right then and there he decided to run. So he began working the room, shaking hands.

''I said, 'Hi, I'm Mark Rosenthal. I'm running for 983 president,' '' he recalled. ''Everyone was shocked. There hadn't been an election in this local in 20 years.''

Soon, Mr. Rosenthal said, he began receiving death threats phoned to his home. After one threat, he said, he punched in the code enabling him to call back his last caller, only to discover that the call had come from the District Council 37 building, where Local 983 and most other locals have their offices. Fearing for his safety, he went to the Federal Bureau of Investigation and the Manhattan District Attorney.

In the balloting for the local's presidency in July, Mr. Rosenthal received 292 votes, Mr. Taylor, the incumbent, won 33 votes, and James Dickens, a vice president under Mr. Taylor, received 161.

''I don't think in the history of the world an incumbent ever received so few votes,'' said Mr. Rosenthal, who has provided the District Attorney with documents about his predecessor's finances.

Thanks to his victory, Mr. Rosenthal is now making $74,367 a year -- his $30,000 Parks Department salary, $35,000 from the local and $9,367 for expenses.

Mr. Rosenthal has rapidly won the respect of those fighting corruption in the labor movement. ''He's the real thing,'' said Carl Biers, executive director of the Association of Union Democracy, a nonprofit watchdog group. ''He's a rank-and-filer who got fed up with a union that was not representing its members and was stealing money. He got involved, he put together an impressive interracial electoral slate and he won. It's encouraging to see this sort of thing emerge.''

Mr. Rosenthal occasionally hires one or two off-duty police officers to sit in at union meetings because he fears some of his opponents might get carried away. He said he would much prefer having the anticorruption fight behind him so he could concentrate on other matters.

He called it scandalous that thousands of city workers were being hired and promoted without taking civil service exams. (''We need that to stop nepotism and favoritism,'' he said.) He is also alarmed that the number of full-time Parks Department workers has plummeted as the number of workfare workers in the parks has soared.

''This union has failed the workers,'' Mr. Rosenthal said. ''They allowed the replacement of civil servants by workfare. They allowed the privatization of many services. They didn't fight as hard as they could.''