President Bush, asserting that the House-Senate conference on clean air has "strayed significantly" and is moving too slowly to pass a bill this year, yesterday proposed a compromise package intended to break what he described as a legislative logjam.

"I fear that the slow progress and apparent course of the conference committee may jeopardize enactment of this critically important legislation," Bush said in a letter to conference leaders.

White House officials described the president's intervention in the two-month-old conference as necessary to light a fire under conferees in the dwindling days of the 101st Congress. The lawmakers have agreed on a handful of noncontroversial measures, turning only recently to the more politically loaded issues of automobile pollution, acid rain, alternative motor fuels and airborne toxics.

But Democratic conferees denied that an impasse has developed and called Bush's letter a political ploy to insulate him from criticism if the bill fails to pass before Congress adjourns. Instead of casting blame, they said, Bush should help fend off industry lobbyists whose pleas for concessions cause the delays.

"I have every confidence we're going to get a clean air bill on the president's desk," said Rep. Henry A. Waxman (D-Calif.), a key House conferee. "I don't feel it's helpful to reopen issues where we already know the administration's point of view."

Bush's proposal, laid out in a three-page memo, does not attempt to resolve differences in the House and Senate bills. Rather, it suggests that conferees accept different provisions of each bill.

In most cases, the president recommends adoption of the weakest provision in each bill. Despite his complaint of slow progress, he suggests that conferees reconsider one of their few agreements -- the House's strong controls for industrial sources of smog -- in favor of the weaker provision passed by the Senate.

Even though the Senate bill represented an agreement with the administration, Bush favored the House provision on controls of auto pollution. It allows an extra year for a first phase of cutbacks in tailpipe emissions and makes a second phase of cutbacks less likely than the Senate measure.

"It's the least-common-denominator clean air bill," Daniel Weiss, of the Sierra Club, said of yesterday's compromise proposal.

Since he introduced a clean air bill last July, Bush has stressed the need to contain costs, threatening to veto excessively costly legislation. He reiterated that concern yesterday, warning that any bill presented for his signature "abide by certain principles."

He said he will not accept "extraneous and costly provisions that are unrelated to clean air," which, aides said, include a $250 million retraining program passed in the House for workers laid off because of the legislation. Another program he opposes is the Senate requirement, estimated to cost $2.5 billion, that would require autos to limit carbon monoxide emissions in cold weather.

According to Roger Porter, the president's domestic policy adviser, the package would shave $3 billion from the $25 billion price tag estimated for both House and Senate bills.

"It would be a terrible shame, and a disservice to the American people, if the prospects for cleaner air were to be scuttled because of a continuing impasse in the conference, or because of the addition by the conference of restrictive and inefficient provisions that saddle the American people with additional costs but yield no additional environmental benefit," the letter said.