In the first political test of energy conservationism since the Persian Gulf crisis, the Senate yesterday effectively killed a measure that would have required cars to get 40 miles per gallon of gasoline by the year 2001.

Sponsors of the measure, touted as a major step in decreasing U.S. reliance on Mideast oil, failed to get enough support to end the threat of a filibuster and bring the bill to a vote. With so little time left in the session, they said they would not try again to muster the 60 votes needed for cloture.

Yesterday's 57 to 42 vote in favor of cloture came after heavy lobbying by the Bush administration and the auto industry against the tougher standards. They argued that the bill would cripple U.S. automakers, cost thousands of jobs and eliminate family-size cars in favor of unsafe, subcompact models.

The lobbying blitz, featuring pleas to senators by local car dealers and auto workers, advertisements, telephone calls from Bush Cabinet secretaries and a visit yesterday by White House Chief of Staff John H. Sununu, reversed the sizable majority -- 68 to 28 -- that voted 11 days ago to bring the bill to the floor for debate.

"They rolled out the heavy artillery," said Sen. Richard H. Bryan (D-Nev.), a cosponsor of the bill. "Our energy security will continue to be jeopardized."

The measure, which would have required automakers to boost fuel efficiency 20 percent by 1995 and 40 percent by 2001, was originally packaged in the clean air bill passed by a Senate committee last year. It was sold as a way to decrease tailpipe emissions of carbon dioxide, which causes global warming.

Unpopular with Detroit and the administration, the provision was dropped on the Senate floor in March. But Iraq's invasion of Kuwait Aug. 2 and its threat to Western oil supplies gave new life to the initiative. The rationale changed from environmental protection to energy conservation, with savings of 2.8 million barrels of oil a day projected by 2005 -- more than three times the quantity of oil imported from Iraq and Kuwait before the invasion.

Motor vehicles consume 60 percent of U.S. oil.

The bill was designed to toughen the Corporate Average Fuel Economy standards approved by Congress during the oil shortages of 1975. Those standards required a near doubling of fuel economy to the current level of 27.5 miles per gallon over a decade.

"No single proposal can do more to ensure the independence of the United States and our security in a world still not as peaceful and orderly as we'd like," Sen. Slade Gorton (R-Wash.), a cosponsor, said before yesterday's vote.

The auto industry, whose campaign contributions and nationwide network of car dealers and auto plants make it one of the most powerful lobbies on Capitol Hill, predicted disaster if the bill passed. A price tag of $62.5 billion over five years was projected, and automakers said they know of no way to achieve the 40-mpg standard without "downsizing" cars so small that safety would be compromised.

"Yes, you can have smaller, more fuel-efficient cars, and a family of 6 or 7 will buy a second car," said Sen. Donald W. Riegle Jr. (D-Mich.), whose state is the nation's leading car producer.

Administration officials stressed that tougher standards would hurt Detroit's competitiveness against foreign producers that specialize in small cars.

Voting against cloture yesterday were eight Republicans who had voted Sept. 14 to allow the Senate to take up the measure for debate. Three Democrats switched.

"It's fair to ask the administration, 'What is your plan?" Bryan said after the vote. "If not this, what?"

The EPA claims that provisions in the clean air bill now in conference, including requirements for alternative motor fuels in smoggy cities and tough limits on oil-burning utilities, will eventually save more oil than the nation imports from Kuwait and Iraq.