Another leaked draft of the administration's Clean Air Act position appears to contradict earlier promises and loosen controls on air pollution further than previously contemplated, key congressmen charged yesterday.

Releasing 78 pages of legislative language dated Aug. 20 and compiled in the Environmental Protection Agency, Reps. Toby Moffett (D-Conn.) and James J. Florio (D-N.J.) said the draft "grossly violated" principles that EPA Administrator Anne M. Gorsuch annnounced Aug. 5.

Unlike previous drafts, the new version would apply cost-benefit analysis to setting health standards, weaken controls over toxic air pollutants and allow more pollution of air in parks and wilderness areas, the congressmen said.

These three principles, particularly not tying air standards to cost-benefit analysis, are particularly important to environmentalists.

It also appears to block any efforts by Canada to sue over U.S. acid rain pollution by restricting suits to "citizens" instead of "persons" and requiring disputes with foreigners to be settled only by treaty.

"These proposals make a mockery of the administration's efforts to portray itself as supporting an effective Clean Air Act," the congressmen said. "The administration still has not perceived the broad public support for clean air legislation."

EPA spokesman Byron Nelson said that despite the draft language, health standards will not be subjected to cost-benefit analysis. "That was confirmed in a Cabinet meeting with President Reagan, and no matter what any draft says, that is the policy on that point," he said.

"This just shows you drafts are only drafts."