WASHINGTON – Martin Frost, the former Texas congressman, dropped out of the race for Democratic National Committee chairman yesterday after failing to win the backing of organized labor, winnowing the field to front-runner Howard Dean and three challengers.

Mr. Frost’s decision came hours after AFL-CIO leaders decided not to make an endorsement in the race for Democratic National Committee chairman.

Mr. Frost had counted heavily on organized labor to give him a boost against Dr. Dean. Many in the AFL-CIO were prepared to back Mr. Frost at one point, but he had not shown enough movement in the race to win labor support, union officials said.

Mr. Frost said yesterday he had called Dr. Dean, the former presidential candidate, and “congratulated him for running a strong campaign. The challenge ahead for Governor Dean will be to unite the party, rebuild the DNC, and win elections in every region of the country.”

Frost aides said the Texan did not endorse a candidate in the race. Earlier in the day, David Leland, former chairman of the Ohio Democratic Party, dropped out and endorsed Dr. Dean.

Democratic activist Donnie Fowler’s campaign was fighting on,along with activist Simon Rosenberg and Timothy Roemer, a former Indiana congressman.

“The AFL-CIO denied Dean their endorsement today,”said Kirsten Powers,a Fowler spokeswoman. “This race has only two candidates who have produced any votes among DNC members so far – Fowler and Dean. At this point only one-third of DNC members have expressed their commitment to a candidate.”

Yesterday, Mr. Fowler’s campaign announced Pennsylvania Democratic chairman T. J. Rooney, a state lawmaker, was backing Mr. Fowler.

Roemer spokesman Ruben Pulido said the former member of the 9/11 commission is staying in the race because Democrats need an effective spokesman on national security issues who will welcome more voters into the party. Aides to Mr. Rosenberg were not available for comment.

At the AFL-CIO political committee meeting yesterday, “some were for Dean, some for Frost, but they didn’t want to get into a contest. We thought the best position for the American labor movement, let the delegates and individual unions decide for themselves,” said Gerald McEntee, president of the American Federation of State, County, and Municipal Employees and chair of the AFL-CIO political committee.

“At this juncture, I believe it’s a fait accompli,” Mr. McEntee said of Dr. Dean’s bid to become DNC chairman.

The motion not to endorse was made by Harold Schaitberger, president of the International Association of Firefighters, who said the union didn’t want to appear like an extension of the Democratic Party.

“We’re confident we have support from DNC members affiliated with labor organizations, but we will continue to work hard to gain support,” said Dean spokeswoman Laura Gross.

The AFL-CIO decision came a day after state party leaders endorsed Dr. Dean. Wellington Webb, the former mayor of Denver, dropped out of the race and endorsed Dr. Dean on Monday.

Amid the jockeying for party chairmanship, rank-and-file Democrats gathered in Washington for closed-door meetings about what the party did right and wrong in the 2004 presidential election.

“A lot of the things we did were right and a lot were wrong,” said outgoing chairman Terry McAuliffe after addressing the group. “The next two days are about discussing our best practices. Let’s pick each others’ minds before we scatter to the winds.”

Democrats will discuss strategies for a handful of statewide elections in 2005 plus the 2006 midterms and the 2008 presidential election.