Two prominent Republican governors threw their support behind the presidential candidacy of Sen. Howard H. Baker Jr. today -- encouraging the underdog aspirant to say, "My realistic goal is to win" the Feb. 26 New Hampshire primary.

Baker shared the stage at a news conference here with Gov. Robert D. Ray of Iowa and Gov. Richard Snelling of Vermont, both longtime admirers of former president Ford, who jointly endorsed Baker today.

Ray, the nation's senior governor with 11 years of service, and Snelling, the current chairman of the Republican Governors' Association, said they had chosen Baker because of his electability, his integrity and his long support of general revenue-sharing and other measures to strengthen state and local governments.

Their move -- which had been expected since last weekend -- marks the first significant intervention in the 1980 contest by the group of 19 mostly progressive Republican governors. Baker's home-state governor, Lamar Alexander of Tennessee, had endorsed his candidacy earlier, and Gov. Charles Thone of Nebraska is backing Ronald Reagan.

But Republican governors in such key states as Pennsylvania, Ohio, Indiana, Michigan, Illnois, Wisconsin and Texas are all avowedly neutral. Snelling, who said he has talked to most of them, said he expected no mass movement in the direction of any candidate. "They will come to their own conclusions in their own time," he said.

Today's news conference was a major part of Baker's effort to convince New Hampshire voters that he remains a viable candidate, despite his third-place finish behind Reagan and upset winner George Bush in last month's Iowa caucuses.

Ray, who lent Baker some staff help but remained publicly neutral during the Iowa campaign, pointed out that all Bush won in Iowa was a straw vote among those attending the caucuses and that Iowa has yet to choose any national convention delegates.

Snelling said that 'As a New Englander, I rather resent the notion that once the straw ballot in Iowa is taken, the nominating process is over."

Snelling acknowledged that polls show Baker trailing Bush and Reagan in Vermont, which holds an advisory primary on March 4, but added, "I don't give a damn. The question is who should be president of the United States."

Baker said he thought he was in third place in New Hamsphire as well, but said, "There is a realistic chance I can convince people that the momentum George Bush earned in Iowa ought not to determine New Hampshire. There is a realistic chance I can finish second here or even win."

Ray, a Ford backer, served as platform chairman of the 1976 Republican convention.

Last fall Snelling was promoting a move to draft Ford as the 1980 nominee, but he said today he gave up that effort when Ford removed his name from the March 4 Massachusetts primary ballot. "I don't want there to be a deadlock," he said, "and President Ford has made it clear he does not want his name considered during the process of the primaries."