The three veteran entertainers standing triumphantly in the spotlight last night, their faces grown craggy through the years of playing the crowds, once stood at the pinnacle of national adulation.

At 68, one is now the Republican Party's shining star, even here in Massachusetss which gave him a frosty political reception four years ago.

And the two black-tuxedoed singers flanking him still command the clout beneath the rusting vocal phrasing of one and the tired simulated drunken antics of the other, to attract over $250,000 for their old show business buddy.

"Why do I support Governor Reagan? Because I think he's the proper man to be the president of the United States," said Frank Sinatra, in his familiar Hoboken accent. "It's so screwed up now, we need someone to straighten it out."

Dean Martin straightened up for the moment and peered out into the crowd. "The only reason I'm here is for Mr. Reagan. Hellooo, Ronnie -- he knew when to quit pictures, boy."

Former California governor Ronald Reagan and his wife Nancy sat front row center, chatting and smiling frequently. The reagans took the stage briefly at the end of the show to thank the two singers and deliver a political spiel. It was the first major fund-raiser in the Northeast for Reagan's expected 1980 presidential campaign.

About 4,000 people said $25, $50, $100 and $1,000 to watch Sinatra and Martin trip through a litany of middle-of-the-road hits.

Standing over a portable bar at the center of the stage and reading from index cards, the two closed the show with a clowning routine in which one played the straight man while the other crooned a response.

Sinatra: "What's Jerry Brown gonna say when all the votes are counted?"

Martin: "California, here I come. . . " Martin: "Hey Frank, what does Ted Kennedy do at night?"

Sinatra: "Dream the impossible dream. . ."

Surrounded by reporters and photographers before the show, Sinatra said he has no allegiance to the Kennedy family though he was an early campaign backer of President John F. Kennedy.

"Jack Kennedy had the presence and aptitude for making a very good president, and I don't know what Ted has the same knowledge as Jack," he said.