New York ? Former Vice President Al Gore will endorse Howard Dean for the Democratic presidential nomination today, a move that could tighten Dean’s grip on the front-runner’s position and win more support from wary party elite.

Gore, who won the popular vote but lost the electoral vote in the disputed 2000 election, agreed to appear with Dean in New York and then travel with the former Vermont governor to Iowa for a formal endorsement, several Democratic sources said Monday.

Dean was coy about the endorsement, telling several hundred supporters at a Manhattan fund-raiser late Monday he could “neither confirm nor deny” it.

The endorsement is a breathtaking victory for a candidate whose anti-war, anti-establishment candidacy has given pause to party leaders and key constituencies, several Democratic strategists said.

“What this says is that all these Washington insiders who have been gnashing their teeth, wringing their hands and clinging to their cocktail cups can relax now. Dean’s been knighted by the ultimate insider,” said consultant Dean Strother of Washington. “It’s game, set and match. It’s over.”

Other Democrats offered more cautious appraisals, but the consensus was that Dean’s coup made him the overwhelming favorite to claim the nomination.

The Gore endorsement comes just weeks after two key unions — the Service Employees International Union and the American Federation of State, County and Municipal Employees — endorsed Dean. The approval of Bill Clinton’s No. 2 bolsters Dean’s case that he represents more than an Internet-driven outsider relying on the support of largely white, upscale voters.

In choosing Dean, Gore bypassed his own vice presidential pick in 2000, Sen. Joe Lieberman of Connecticut. The Lieberman campaign issued a terse statement Monday, saying, “I was proud to have been chosen by Al Gore in 2000 to be a heartbeat away from the presidency,” and added, “Ultimately, the voters will make the determination and I will continue to make my case about taking our party and nation forward.”