John Edwards added the Transport Workers Union to his array of organized labor support yesterday, accepting an endorsement from the 34,000-member local from its president, Roger Toussaint, at an event in Midtown.

The TWU said the former senator from North Carolina is the Democratic presidential candidate with the best chance of winning the 2008 general election.

“Hillary gives Republicans their best shot to keep the White House,” the union said in a statement, referring to Senator Clinton, the Democratic front-runner. Mr. Edwards is the only leading Democratic candidate who has a statistically significant lead over the top Republican candidate, Mayor Giuliani, union officials added.

“If we are going to strengthen the middle class in America, it is critical that we strengthen the union movement in America,” Mr. Edwards said at yesterday’s rally. He also said he wanted to make union registration more accessible and ban the hiring of permanent replacements for strikers.

It was unclear how much sway the union’s support would have in the city’s Democratic presidential primary.

“Conceivably, a few people don’t like Mr. Toussaint and that spills over,” a labor historian at the City University of New York, Joshua Freeman, said, referring to Mr. Toussaint’s tactics during the transit strike he led in 2005.

Still, despite almost universal condemnation on the editorial pages of the city’s newspapers, Mr. Toussaint had a “fair amount” of public support during the 2005 strike, Mr. Freeman noted.