James A. Baker III yesterday easily won confirmation from the Senate to be the 67th secretary of the Treasury, allowing him to swap jobs next week with Treasury Secretary Donald T. Regan, who will take over Baker's job as White House chief of staff.

The Senate voted 95 to 0 to confirm Baker, a Texas lawyer and behind-the-scenes architect of many of President Reagan's legislative victories. Baker's major opponent had been Sen. William Proxmire (D-Wis.), who said that Baker may have been qualified for other jobs but not that of Treasury secretary. Proxmire voted for Baker, although he said he did so with "grave misgivings."

Baker will not officially become Treasury secretary until he is sworn in. A swearing-in date has not been set, according to a White House spokesman. However, other administration officials said they expect Baker to take over his official duties in a few days.

During Baker's confirmation hearing last week, and also in the one-hour debate today on his nomination, Baker was praised for his past accomplishments and skillful negotiation of the president's domestic agenda.

"What you want is a man of intelligence, and you've got it in Jim Baker," said Senate Finance Committee Chairman Bob Packwood (R-Ore.) "I can think of no one . . . who is better suited right now than Jim Baker."

Senate Majority Leader Robert J. Dole (R-Kan.) said, "We'll have a lot of work to do in the next few weeks and months dealing with the Treasury secretary. I'm convinced we can rely on constructive assistance from the distinguished nominee."

In other action, the Senate Finance Committee unanimously approved the nominations of Richard G. Darman to be deputy Treasury secretary and of Ronald A. Pearlman to be assistant Treasury secretary for tax policy. Darman is assistant to the president, and Pearlman is acting assistant secretary for taxes.

Darman, in testimony during his confirmation hearing yesterday, reaffirmed the Reagan administration's commitment to keeping tax simplification a priority equal to reduction of the federal budget deficit, despite recent warnings by prominent Republican senators that tax changes will have to take a back seat to budget cuts.

On Monday, Republican congressional leaders, after a one-hour meeting with the president, said that the White House planned to delay submitting a tax simplification bill to Congress for several months. Packwood has said that his committee and the House Ways and Means Committee want the tax proposal to wait until action is taken on the administration's plan to reduce the federal budget deficit by $51 billion.

Darman said the administration does not plan to delay action on the tax simplification proposal into 1986, as some administration officials have said privately. Even if a tax bill is formally submitted later this year, that doesn't necessarily mean that the whole congressional process would be delayed, Darman said. He added that Congress could go ahead and hold hearings on tax reform proposals at the same time that the deficit is discussed.

Darman said that the next time the administration presents a tax proposal it will "have wider support than that one on the table now," meaning the plan submitted by Regan.

"Assuming a proposal is developed in the next couple of months, the process could go well," Darman said. The administration is interested in moving on deficit reduction and tax reform "as expeditiously as possible. We specifically do not want them to be joined. We do not think that one need necessarily wait at one stage or another for the other. Each can move on its own track as fast as it can."

In other remarks, Darman said that high U.S. interest rates and the federal budget deficit were not the reason for the dollar's record strength, nor was that strength necessarily all bad. Darman said the administration should focus on promoting growth in other countries to help solve the dollar problem.