George Bush's campaign manager came to Washington yesterday to dampen the expectations of a Bush victory over Ronald Reagan in the Feb. 26 New Hamphire primary.

The way James A. Baker III told it, Reagan is so beloved and others so active in the Granite State that Bush will be lucky to survive the test.

"Our goal," he told a tableful of somewhat incredulous reporters, "is the same as in Iowa -- to finish a good strong second."

The prospects of Bush repeating his Iowa caucus victory over Reagan are minimal, Baker said gravely. "New Hampshire is Reagan's strongest state in the Northeast. He has a solid base of 27 to 30 percent of the vote. It's a multi-candidate field and Baker [Sen. Howard H. Baker Jr.] will draw much more heavily from Bush than Crane [Rep. Philip M. Crane] will draw from Reagan."

Seeing undisguised skepticism over the remains of the scrambled eggs, the Bush manager said: "You won't believe this, but I honestly believe what I'm telling you."

He even offered to bet anyone who expected a Bush victory.

What James Baker was doing was part of the ritual of "expectation politics," known to football coaches, fight-managers and other such specialists in the manipulation of opinion.

Bush has been on the excess escalator up since he ambushed Reagan by 2 points in Iowa.Two quickie national polls have shown him nearly even with Reagan, and the publicity surge is just beginning. But his campaign staff knows he could fall just as fast if New Hamphire reverses the order of finish -- as it might -- and if the setback is unexpected.

Thus, the campaign manager's efforts to lower expectations.

John P. Sears, the Reagan manager said in a separate interview that a pre-Iowa poll of New Hampshire showed Reagan ahead of the field and added: "We feel we're strong in New Hampshire and if we do what we're capable of doing, we should be all right."

But a poll taken for another candidate showed "real softening" in Reagan's New Hamphire support even before the Iowa caucuses. The poll was taken the weekend before the Iowa vote. Allocating the undecided voters on the basis of expressed attitudes toward the candidate, this survey gave Reagan 43 percent; Bush 31; Rep. John B. Anderson 11, and Baker 9, with Crane, John B. Connally and Sen. Bob Dole receiving only a scattering of votes.

As in Iowa, Reagan has a campaign organization left over from his 1976 race, when he nearly defeated former President Ford. But Bush was the first of the 1980 challengers to organize New Hampshire, and he picked up a broad array of Ford backers -- plus former governor Hugh Gregg, Reagan's 1976 campaign chairman.

Bush has spent more than 40 days of campaigning in New Hampshire already, and according to James Baker, will spend only eight more days there before the primary. by contrast, Sears said Reagan would campaign 12 or 13 days in New Hampshire. Sen. Baker has committed 20 days to the state, which also will be the focus of most of the Crane and Anderson activity in February.

Both Reagan's and Bush's campaign managers said they expect that a debate will be arranged among all the Republican candidates in New Hampshire. Reagan's refusal to join the others in an Iowa debate was criticized in that state and blamed by some for his upset at Bush's hands.