Senate Republican leader Howard H. Baker Jr., setting a sharp partisan theme for his first intensive presidential campaign swing, today called on President Carter to "depoliticize the White House" by withdrawing from the presidential race.

Baker said he thought it was "the only way to restore credibility" in Carter's decisions now that the president "is so far down in the polls."

Baker coupled that advice with a wholesale attack before the Missouri Farmers Association on Carter's performance and policies - foreign and domestic - with emphasis on energy and the SALT pact now being considered in the Senate.

"Some of my critics are fond of saying that SALT should be above politics," the Tennesseean told the farmers. "But I believe that politics has in fact played a major role in causing this administration to enter into a bad deal because it was the only deal they could get in time for the election year. Maybe it is good politics. I guess we'll see, but it is horrible security policy."

Baker, who as Senate minority leader is leading a fight to send SALT II back to the negotiating table for more concessions from the Soviets, told the farmers that the president "seems constantly preoccupied with the politics of 1980 rather than with the responsibilities of leadership."

In an interview, Baker said he would pound on this theme for the next month, as he campaigns in 25 states.

The president is having such political difficulties, Baker said after the speech, that the purpose of every major decision he makes can be held up to question. Withdrawal from the race, he said, would be the only way to "salvage" and "restore confidence" in these decisions.

Though he has yet to declare his candidacy, Baker's speech and this month-long trip which began here today represent his formal coming-out as a presidential hopeful.

The speech also reflected the now dominant view among most republican contenders that they must target Carter for attack - at least for the moment - rather than go after each other.

"There is the litany of a country in trouble," Baker said in what is expected to become his standard campaign speech: "A bad SALT II treaty, an outmoded strategic arsenal, an international reputation for bumbling diplomacy or inaction or both, a crumbling world dollar, an energy shortage without answers, the highest interest rates ever, growing unemployment, soaring inflation and, finally, a recession growing worse daily."

Amid it all, he said, "we have an administration preoccupied with its own reelection and apparently incapable of leadership."

"The president says that we have lost confidence in ourselves," Baker said. "I think he's wrong. We have lost confidence in the White House.

"The president cites past administrations and past mistakes and past traumas. I think he's wrong. Surely we've experienced a tough 16 years," Baker said.

"But our lack of confidence today relates to today's traumas and today's mistakes and today's administration.

"...There is growing sentiment for Mr. Carter's resignation. That isn't going to happen and would make things worse if it did. Playing musical chairs with the Cabinet is destabilizing enough; playing musical chairs with the Oval Office would assure total choas,

"...If I were President Carter today, I would announce that I would not seek reelection. That would depoliticize the White House and give more credibility to the president's program."

Baker also repeated his energy and inflation proposals, including "more attention to solar, nuclear and geothermal heat as long-range energy answers."

He also called for appointment of Henry A. Kissinger as an American representative to a proposed "North American common market for energy and power resources" and for the appointment of Carter's Mideast ambassador, Robert Strauss, to handle White House policy coordination and congressional relations.

Baker endorsed Republican proposals for a major income tax cut to combat recession and for complete decontrol of gasoline prices "the moment the windfall profits tax is passed."