It is 100 degrees at the Fort Smith GOP picnic. The candidate drenched with sweat, takes off his jacket, rolls up his sleeves, sings the National Anthem, thanks the Girl Scouts for coming and begins his race for the presidency.

Waving an arm, Sen. Howard H. Baker, (R-Tenn.) talks about free enterprise, economic growth, about "making America so strong that none dare challenge her," and about "getting the government off our backs."

He also talks about putting a Republican - any Republican - in the White House. "We've got the candidates. Good grief, have we got the candidates. And any one of them on a bad day is better than Jimmy Carter on his best."

The theme was the same wherever Baker went last week - Arkansas, Iowa, Illinois, Missouri and Florida. He finally had begun intensive campaigning after months of being what he calls a "weekend warrior" who had to tend to his duties as Senate Republican leader during the week. Over the next three weeks Baker will visit 21 more states and Puerto Rico in his attempt to win the Republican presidential nomination.

His first week showed that he was not moving to the right, as some expected, and he was certainly not moving left. What he was doing was smoothing out the wrinkles, like his Panama Canal treaties vote, and mainstreaming it for all he was worth.

"Sensitizing" was the work Baker used to describe his mission this month. "I've got to sensitize people now so they know I'm for real. That's what I'm doing.

Davenport, Iowa - An early morning breakfast organized by Baker supporters has drawn about 300 Republicans, independents and a few Democrats. On the table, underneath the orange juice at each place setting, is a copy of a newspaper article reporting the latest Harris poll.

It places Baker in that magic circle with Ronald Reagan. He can beat Jimmy Carter, the poll says.

"The keynote of my campaign," he tells the breakfast, "will be electability. Any party which claims the allegiance of 18 percent of the voters has to reach out beyond party boundaries.

"I was the first Republican senator elected in Tennessee. I have always been elected with support from Democrats and independents.

"And in the Senate, as leader of the Republicam Part , I have welded together 41 senators ranging fro. Jesse Helms on the one hand to a Mac Mathias and Jack Javits on many issues."

Back in his small chartered jet on the way to the next stop he elaborates. "It's not necessary to have a cause that distinguishes me from the other candidates," he says. "Electibility is the way I'm going to do that."

True, he says, the same polls that show Baker beating Carter also show Reagan beating both of them.

"But Ronald Reagan," he says, leaning closer, knowing you'll understand what he's about to say, "is Ronald Reagan."

"After I travel the country, after I announce in particular, after there's a clear-cut choice, that phenomenon will have its effect.

"They'll see an alternative.

"The big thing Reagan has going for him now is momentum," Baker says. "And that's left over really from 1976, and it's name recognition left over from 1976.

"As these things begin to diminish, I think the numbers will begin to change."

Tampa, Fla. - The money is gathered around the table and most of it hasn't been wagered yet for 1980. About 40 of Tampa's wealthiest businessmen have assembled for a low-key lunch with the senator.

They are all regular Republican contributors. It says so in a carefully prepared dope sheet Baker's aides study before the meeting. One of the men, it says, has given $105,000 to Republican candidates.

It is by now accepted by all the Republican candidates that they will not tear down the others in public. "I'm not running against any of them," Baker tells these businessmen.

But, he says, not mentioning Reagan by name, "The party needs a new face. I'm not that new, but I'm newer than some."

Besides, he says, "I don't think the party wants a rerun of 1976."

Back on the plane he deals with John Connally. "John Connally is a flirtation for many Republicans. And I don't think it's going to lead to a marriage." Earlier he has told businessmen in Chicago that George Bush would make a fine secretary of state. "He'll be very angry at me for saying that."

But the businessmen are asking not about Reagan, Bush, Connally and the others but about economic policy and energy.

The answers Baker is giving are about "free enterprise," about the need to allow industry to produce without a lot of government interference.

In energy policy, he says, it follows that oil must be decontrolled, the allocation system junked, the Department of Energy abolished and revenues from windfall profits tax plowed back into production, not into government coffers.

The government must cut spending, cut taxes and balance the budget even if ti takes a constitutional amendment to do it, he tells the businessmen.

Des Moines, Iowa - The setting is the Iowa Farm Bureau Federation Board of Directors meeting.

They're telling Baker about the ungodly ceiling the government has placed on grain prices. Howard Baker is telling them about the Strategic Arms Limitation Treaty (SALT) now before the Senate.

He has it boiled down now to what he feels are more intelligible dimensions - without too many numbers and too much jargon.

"Some people say, "Senator Baker, we'd better vote for that treaty or we're gonna make the Russians mad,"" Baker tells the farmers. "Well, I'd rather make 'em mad today instead of 10 years from now when they're stronger than us because of some decisions we made today."

"I'd hate to see us toe to toe with the Russians in 1981 or 1982 in another Cuban missile crisis," Baker says. "I'd hate to see us be the ones who have to blink first."

He then explains that he's holding off his decision on how to vote on the proposed treaty until amendments are passed that satisfy his apprehensiveness America's military position.

But in Des Moines, in Davenport, and in Fayetteville, Ark., SALT was "That's for the big people in Washington to decide," said Sam Phillips, a Fayetteville Republican Party worker.

"It surprised me a little," said Baker, who had counted on it as a major and useful theme. "It is a clear third or fourth on the scale of importance with inflation and energy a clear one and two."

Miami - The major wrinkle, wherever he went but expecially here in Florida, was his vote in favor of the Panama Canal treaties. He was asked about it at every stop and explained his position with the same answer.

He explained that what he really did by successfully proposing amendments to the treaties was in fact to strengthen America's control and its ability to defend the canal. "What we gave up," he says, "was the legal title to the canal.

"What we got was a better treaty than we ever had." CAPTION: Picture, Sen. Howard H. Baker