A nattily-attired Elliot L. Richardson '41, sitting with legs crossed, pauses over his salad at Boston's Cafe Tremont, looking like anything but a man about to embark on a grueling, and possibly bitter, fight to become a senator from Massachusetts.

"I'm not one of those candidates who sits at the head table and lets all the food go by." Richardson says, introducing his theory of campaign dieting.

Richardson, the best known and most highly respected of the state's few Republicans, may be the most blase candidate ever to seek such high office.

At age 63, Richardson approaches the race from a completely opposite perspective than do his three main Democratic rivals, all reformers in their thirties who are just beginning to gain attention outside the state.

Richardson held a variety of top and middle-level administrative posts in Washington throughout the 70s, and, according to various accounts, even played with the idea of running for President in 1980.

"He could take it or leave it," says one long-time friend. "The Senate seat is almost like a consolation prize."

A Boston Brahmin's Boston Brahmin, Richardson assures voters that he will have instant seniority upon reaching the Senate floor, merely by dint of the many connections he has made serving a number of Presidents--most recently Jimmy Carter--over the past three decades.

Richardson also makes no secret of the fact that officials in the highest circles of the Reagan Administration pushed him to run for the nomination against eccentric businessman Raymond Shamie, after the popular Sen. Paul E. Tsongas (D-Mass.) announced his retirement from politics in January.

Richardson is confident the party establishment is behind him, even though he wavers considerably from the Administration line on a number of foreign policy matters.

"They view with some seriousness the objective of maintaining Senate control," Richardson says. "They think I'm the only Republican candidate who has a strong chance of winning."

But though the Harvard alumnus insists he supports "the main thrust" of Reagan's foreign policy agenda, his campaign takes on a moderate and sometimes liberal tone.

Richardson, for instance, criticizes a nuclear freeze--because it doesn't go far enough.

He calls for the declaration of a new Monroe Doctrine that would bar both superpowers from intervening militarily in Central America, placing a greater emphasis on the United Nations to mediate Thil I World conflicts.

He calls his role in the inconclusive Law of the Sea Treaty one of his greatest achievements, even though Reagan successfully undermined the proceedings.

Though Richardson concedes that he must work hard to appeal to state Democrats--Massachusetts is, of course, one of the strongholds of old-line liberalism--he soft-pedals discord between himself and the Reagan Administration, whose hard-line policies, he claims, are more bark than bite.