Washington ? Two powerful unions formally endorsed presidential hopeful Howard Dean on Wednesday, further cementing his status as Democratic front-runner by nearly every measure — organization, momentum and money.

Dean’s political coup came in a rare but expected joint announcement from the presidents of the American Federation of State, County and Municipal Employees and the Service Employees International Union, in a carnival-like event that overflowed with hundreds of patriotic, flag-waving, cheering union members.

“This man of Vermont has the best chance to beat Bush,” said Gerald McEntee, president of AFSCME, which counts 1.5 million members.

Dean, a physician, has successfully used the Internet to outpace his rivals in fund raising, and has attracted large, boisterous crowds. In particular, he has caught the attention of voters outside the traditional Democratic Party base, making his candidacy attractive to McEntee and SEIU President Andy Stern.

“After November 4th, there will be a doctor in the house — the White House, that is,” said Stern, whose union is the largest under the AFL-CIO umbrella and represents more health care workers than any other.

But Dean still lacks the support of many party leaders; they question whether he has the temperament to win, and worry that liberal aspects of his record will be easy targets for Bush. The fear is that he will follow in the footsteps of White House losers Michael Dukakis in 1988 and Walter Mondale in 1984.

AFSCME’s endorsement was particularly vexing for Dick Gephardt, John Kerry and Wesley Clark — all of whom had at one point thought they had the nod in hand.