The Senate Environment and Public Works Committee reached surprisingly easy agreement yesterday on one of the most controversial of the Clean Air Act provisions, voting to leave unchanged the way current law sets pollution limits.

But the session was an unusual combination of rhetorical free-for-all and legislative markup, leaving the Reagan administration, one of the losers in the vote, free to say that the committee had not yet really decided part of the question.

The administration's "guiding principles" for rewriting the 1970 act, announced in August, would add scientific peer review and risk assessment to the process that now sets ceilings for pollution emissions to protect human health.

Business groups had sought to change the process further by eliminating the "margin of safety" the law requires for the elderly, children and sensitive people. They also want to return to the states the right to set the tighter so-called secondary standards for protection of the environment.

But the committee members ignored these proposals and on a 13-to-0 voice vote approved the recommendation of committee Chairman Robert T. Stafford (R-Vt.) that this part of the law be kept as it is.

Stafford said repeatedly that the purpose of the jammed meeting was only to get "some indication as to where the committee wants to go" in drafting legislative language for approval later. He urged that there be no vote on a second controversial issue, that of automobile standards, "so we can complete this list in an informal manner."

That led Kathleen Bennett, the Environmental Protection Agency's assistant administrator for air, noise and radiation, to say after the meeting that she still expected administration supporters to work risk assessment and peer review into the bill. "I don't think this vote means discussion is concluded," she said.

Richard Ayres of the National Clean Air Coalition disagreed. "We won that one," he said. "I don't think there's a prayer they'll come back on risk assessment."

Discussion barely began on automobile emission standards, but it was clear that this may be a major sticking point.

Sen. Daniel Patrick Moynihan (D-N.Y.) denounced a pending House measure to double the permitted output of nitrogen oxides and carbon monoxide, promising that "if anything approaching" it is adopted by the Senate committee, "there will be no Clean Air Act this year."

But the House measure is strongly supported by Rep. John D. Dingell (D-Mich.), chairman of the Energy and Commerce Committee, which will have to clear any rewrite of the Clean Air Act.

The committee members each aired their priorities. Sen. Alan K. Simpson (R-Wyo.) cautioned that his interest in changing the act did not make him "a slavering beast with a steam shovel in each hand." Sen. Steven D. Symms (R-Idaho) endorsed the administration principles as "a compromise position," while Sens. John H. Chafee (R-R.I.) and George J. Mitchell (D-Maine) called for leaving the act basically alone.

Stafford said Senate Majority Leader Howard H. Baker Jr. (R-Tenn.) has no time scheduled for a Clean Air Act floor debate but "would try to find time for us" before Christmas if the committee promises only a day or a day-and-a-half of debate. That means consensus must be achieved soon, he said.

Stafford continued the hearing to Thursday on auto emissions and five remaining issues: clean air preservation, deadlines for compliance in areas with dirty air, coal-burning plant regulations, controls over acid rain and controls over hazardous pollutants.