The Senate Environment and Public Works Committee voted yesterday not only to retain most current pollution standards for heavy trucks but to convert them from mere regulations into the law of the land.

Three of the changes to the Clean Air Act, offered by Sen. Gary Hart (D-Colo.), would block current or expected efforts by the Reagan administration to loosen motor vehicle requirements through regulatory change.

Hart said he planned it that way. The issues, he said, are among the most important facing the committee in its effort to get a rewrite of the 1970 law to the Senate floor by the end of the year.

On a vote of 10 to 3, the committee agreed to strip the Environmental Protection Agency of authority to change heavy-duty truck emission standards.

The standards now require a 90 percent reduction from 1977 levels in the trucks' hydrocarbon and carbon monoxide emissions by 1984. The EPA, however, said in April it planned to require only a 60 percent reduction. Assistant Administrator Kathleen Bennett told the committee the 90 percent levels could cost the trucking industry up to $450 million.

Hart responded that the number seemed to be "plucked right out of the air" and that in any case economic arguments were not enough.

"The question is whether we want EPA to make an economic decision on a public health issue," he said.

Sen. Alan K. Simpson (R-Wyo.) opposed the amendment on the grounds that it removed administrative flexibility. Sens. Steve Symms (R-Idaho) and Frank Murkowski (R-Alaska) joined him in voting no.

Two other Hart amendments passed by unanimous voice vote. One would enact into law the current regulatory definition of light duty trucks that includes vans, pickups and recreational vehicles such as campers, and would also make a law of the current emission control requirements.

EPA has not yet tried to relax those standards but his amendment would stop them from trying, Hart said. Simpson, Symms and Murkowski went along with this when Hart modified his amendment to ease requirements for agricultural vehicles.

The third Hart amendment would write into law a current regulation limiting diesel vehicles to emissions of l.5 grams of nitrogen oxide per mile by 1983, making it 1.0 grams by 1985.

The only amendment to ease things for automakers was offered by Sen. Lloyd M. Bentsen (D-Tex.) and passed unanimously. It would halve the mileage-warranty requirements for makers of pollution-control equipment and would allow diesel companies four years in which to tool up to meet the upcoming standards for particulate emissions, or soot.

There has been much controversy over whether these particles are possible cancer-causing agents. The Bentsen amendment would require that whatever standard is set continue effective for four years so that manufacturers have some planning time.

The committee will continue its rewriting Dec. 3.