The administration is willing to change some details for its new tax proposal to regain the support of business groups for the congressional fight that begins in earnest this week, White House chief of staff James A. Baker Iii said yesterday.

Baker said that while President Reagan is probably through negotiating with the Democratic leadership on the tax issue, the bargaining with business isn't over.

"I don't think the final details of the program are frozen," Baker in an appearance on "Face the Nation" (CBS, WDVM). He said the gap that opened suddenly between the administration and the business lobbying groups when the new tax plan was unveiled last Thursday is closing.

Cliff Massa of the National Association of Manufacturers agreed, to a point. "I have some reason to believe this will settle down" is there are compromises by the administration and the southern conservatives the administration is trying to win over, Massa said. "It's hopeful speculation at this point, nothing specific."

Meanwhile, House Speaker Thomas P. (Tip) O'Neill (D-Mass.) said his side had some bargaining to do as well, and will try to pry Republican and Democratic House members away from the president's side by forcing separate House votes on half-dozen of the most sensitive spending cuts proposed by Reagan.

O'Neill, interviewed on "Issues and Answers" (ABC, WJLA), cited proposed budget cuts in food assistance for children and the elderly, aid for handicapped children and vocational education, saying, "We're not going to eliminate those programs without a fight."

The House speaker, whose leadership in the economic debate is being questioned by some of his fellow Democrats, hit hard at Reagan, calling the administration tax program a "windfall for the rich."

"The president truly in my opinion doesn't understand the working class of middle America, what it's all about, what they go through, because of the fact he doesn't accociate himself with those types of people," O'Neill said.

O'Neill said he didn't mean that Reagan was "callous", but the speaker said, "I think that he has very, very selfish people around him."

O'Neill's verbal thrusts were parried yesterday by White House counselor Edwin Meese III, who, like Baker, was making a television interview appearance on behalf of the president's tax plan, scheduled to be taken up by House and Senate committees Wednesday.

No one who knows Reagan can believe he is unsympathetic to the problems of working people, the president's counselor said. "The president himself is probably the best example of a working man, a man who came as a child from absolute poor circumstances . . . who worked his way up into a very sizable income through his own hard work," Meese said on "Meet the Press" (NBC, WRC).

The administration's immediate problem is dealing with the business groups whose leaders and lobbyists were jolted by the sudden change in the president's tax program.

Massa said he and his associates still hope to persuade the administration that it is not necessary to cut $50 billion from the business tax reductions in the president's original plan. The reduction was made in part to reduce the drain on tax revenues over the next six years and thus to make it easier eventually to balance the budget, a concession the administration believes is critical to winning the backing of conservative Democrats.

The business groups are also attacking an accounting provision in the administration's new plan that would require some businesses to depreciate investments in equipment over a longer period than called for in the original plan -- plan thus lessening available cash after taxes.

Massa said this particularly hurts the manufacturing industries, including textiles, machinery, chemicals, aerospace and electronics, whose members loudly supported the president's original economic program.

"We want to continue to support the president's program," Massa said. "But we don't need these kinds of problems."