Everywhere he goes these chilly days of January, people tell Sen. Howard H. Baker he is gaining momentum and that after months of traveling under what seems to be a permanent black cloud, his campaign for president is beginning to see rays of sunlight.

But everywhere he goes, the Tennessee Republican is also told it is probably too late to do him much good in the Iowa precinct caucuses Monday night.

Baker accepts this. So he is positioning himself for defeat, lowering expectations whereever he goes.

"The real race is for third place," he told a news conference here Wednesday. "Anything we do better than that is pure gravy."

"Ronald Reagan and George Bush are the front-runners in Iowa. I would do very well indeed to finish in third," he said, adding that Bush has built up the best campaign organization in the state and "George may be THE front-runner."

The idea, of course, is to set a high standard of expectation for Bush, his chief rival for the hearts of GOP moderates, and low expectations for himself. Then if Bush does worse than expected and Baker better, Baker becomes a winner even in losing. John B. Connally, who is running neck-and-neck with Baker for third, has adopted the same tactic, saying Bush is definitely "THE favorite."

Baker is so relaxed, so affable, so skillful at cloaking his motives and qualifications for the presidency in nobility that it is hard to believe he is running for third.

That until recent days he was considered an underdog even for that spot is a biting commentary on the presidential selection process and Baker's inability to adapt to the process.

This election year, Baker's aides tell reporters, wil answer the question, "Can a man hold a job and still run for president?"

The question is valid. Among the top four GOP presidential candidates -- Reagan, Bush, Baker and Connally -- only Baker has held a major elective office in recent years. While Bush went from one small Iowa town to another last year, Baker stayed in the Senate as minority leader.

But the slowness in Baker's campaign development also reflects on his plain bad luck. He adopted an early strategy tied to Senate consideration of the strategic arms limitation treaty (SALT), thinking Senate debate would cast him as a national spokesman for his party. The debate never came. Baker also failed to put together an effective campaign operation and was forced to do a major housecleaning in late November during which he replaced his campaign manager.

The improvement in his stature here is due to three factors: a rescue operation by Gov. Bob Ray, the state's most popular politician, on Baker's state campaign; an effective media effort, and the candidate's performance in recent weeks.

Ray, one of the nation's leading GOP moderates, informed Baker his campaign was in deep trouble in November. And Ray arranged for one of his top political operatives, Dick Redman, to take over the Iowa campaign. Afterward, media spending was stepped up and the candidate spent more time campaigning here.

Opponents concede that Baker's TV and radio ads, designed by Washington consultant Douglas Bailey, have been the most effective in the campaign. They feature Baker shouting down an Iranian student at a rally and a catchy patriotic jingle, "Welcome Back America."

But opponents argue that reliance on ads appealing to a mass audience is a strategic mistake in a state that attracted 20,000 party members to caucuses in 1976. The ads have, however, helped Baker in the polls. His rating in the respected Des Moines Register's Iowa poll rose from 11 percent in December to 18 percent last week.

Since Jan. 1 Baker has spent more time in Iowa than any other candidate -- eight days -- and by Monday he will have logged almost as many days in the state as Bush -- 25 days to 27 -- during the last year.

On the stump, Baker is an impressive orator. He combines a homespun speaking style he learned as a lawyer in the Tennessee mountain village of Huntsville with anecdotes about Washington and reminiscences about his father-in-law, the late Illinois senator Everett Dirksen, "I used to be a lawyer, but I got over it," he says good-naturedly.

He is treated almost with reverence. When he spoke to the Marshalltown Kiwanis Club Wednesday, he was greeted with a song: "How do you do, Mr. President." "We hope you can make it," the club's song leader said. "If we're wrong, well, just forget it."

Baker mentions few specific issues during a standard speech. Instead, he tells audiences, "i want to give you a look inside my head to let you see what kind of president I'd be."

Here are a few snatches: "I believe in a strong presidency. It is a place for a man to lead . . . I am not a detail man. I will not be a yellow pad president . . . I'll be a political president, but I will try to ennoble politics."

The crowd in this highly Republican area of central Iowa loved it. But after the candidate had walked out, his county chairman, Ronald Fenton, a local banker, said he felt Baker would do no better than third in the area.

"We've been at this a very short time here," Fenton said. "I am very encouraged. I think we're causing some people to consider changing their positions . . . but up have to put Reagan and Bush way ahead of Sen. Baker here.