At the party that was synthetic fuels, the champagne has gone flat, the music has slowed and the headaches are beginning. And Uncle Sam, the genial host, has all but stopped handing out aspirin.

The Synthetic Fuels Corp., which held its third board meeting last week, no longer plans to commit $17.5 billion as fast as possible to encourage the industry dance. The Environmental Protection Agency has abandoned its effort to produce a whole new regulatory approach.

And some of the industry participants have gone home, saying the whole bash was getting too dangerous.

The future of the new synthetic fuels industry now appears to depend on the people it was launched to combat: the international oil cartel. If oil prices keep rising, the multibillion-dollar synfuels industry is on its way.

If they don't, it isn't. And right now, prices are stable.

Few analysts believe this stability is anything more than a lull. But no one is sure, and that uncertainty has cooled the rush to synfuels.

The idea in 1980 was to free America from dependence on imported oil by producing liquid fuels from U.S. coal and oil shale deposits. By 1987, President Carter said, we should be producing 500,000 barrels of synthetic fuel a day, and by 1992 2.1 million barrels a day, about half the current oil import level.

The Synthetic Fuels Corp. was set up to obligate $17.5 billion in federal money for price guarantees, purchase agreements, loan guarantees, loans and joint ventures in that order of priority to get the industry going.

Now the corporation's goal has shifted from massive production to making a political point.

Corporation board chairman Edward Noble has said he just wants to get enough plants started to demonstrate to the Organization of Petroleum Exporting Countries that the technologies work and that the product won't blow the U.S. bank book.

"We do need the technology, and if we don't do anything but show we can do it on a certifiably economic basis, it'll have some influence in the prices OPEC will put to us," he said. "It may be cost-effective in a backdoor type of way, kind of a club under the table."

This reversal for synfuels is the result of three factors, according to Mike Koleda, head of the National Council on Synthetic Fuels Production, a trade association of 55 companies.

First, high interest rates have delayed all capital-heavy projects, and each synfuels plant could cost $3 billion to $5 billion.

Second, synfuels plants started now are not likely to have a product that will be cheaper than regular fuel when the plant is finished in five to 10 years.

Oil prices drive construction prices, so for synfuels to be competitive, the price of regular oil must keep rising after the plant is built. And world oil prices "will be flat or at least soft for this decade," Koleda said. Companies are reluctant to invest with slim prospect of success.

Third, the Reagan administration would rather have private industry shoulder this kind of huge financial job. "It's a very basic, dramatic change in policy," Koleda said.

Noble, a major figure in the synfuels drama, is seen as a product of that policy shift. At 53, the soft-spoken Tulsa oil tycoon admits he had to be convinced the government had any role in the industry. "I saw people offering it as a panacea and it isn't," he said. "I told Congress I wouldn't have voted for it."

He still wants government out of synfuels as fast as possible. Although the corporation expects to have $8.6 billion to commit this year, Noble does not plan to use it all, even though one synfuels plant can cost $3 billion or more.

He wants to have money for future technological processes, he said. Projects that win his go-ahead will be the ones that put up the most money.

Some industry figures object. "Why is he in that job if he doesn't want to spend the money?" asked one western oil company official. To this unhappiness, Noble replies: "That's tough. You don't discourage serious people. If they just want a free ride they don't need to come around."

The corporation received 63 applications for help in its first round of solicitations, and last week narrowed the list to 11, from which "a few" will be chosen in March, Noble said. Six projects are small in synfuel terms, aiming at eventual production of less than 12,000 barrels a day.

Even if all 11 are successful, with or without federal help, their production will barely exceed 205,000 barrels per day, a far cry from the original target.

To environmental groups, which think EPA's controls over synfuels are inadequate, the slowing is a great relief.

Noble said the Synfuels Corp. will not fund any project until it complies with environmental rules, but synthetic fuels are something new on the planet and not all are covered by existing rules.

In some tests the chemicals caused alarming mutations, cancers and other damage in laboratory animals. Water used in the processing absorbs dangerous chemicals and must be disposed of properly.

Waste dust as fine as talcum powder must be safely handled and disposed of. But an ambitious EPA plan to produce "regulatory guidance documents" for the industry as it was being born was abandoned last fall after $6 million had been spent.

"Designs were changing so fast on the processes it was impossible to come up with a document that would answer all questions," explained Andrew Jovanovich, acting chief of EPA's research and development office when the program was killed.

The agency, hampered by its stiff budget cuts, now plans only to provide teams of experts to advise state and local officials on permit applications from synfuels projects, Jovanovich said. No such teams exist.

Environmentalists charge this is not enough. "The corporation still has no environmental capacity whatsoever, and nobody at EPA is going to monitor it," said Jonathan Lash of the Natural Resources Defense Council.

Rep. Toby Moffett (D-Conn.) plans hearings on the synfuels regulatory situation next month in his Government Operations subcommittee on energy.

Legislation is pending in Congress to revamp federal oil shale leasing, allowing more acreage per company and providing space to dispose of the waste. But there is no agreement on the size of the expansion or who gets to lease additional land.

The Interior Department has allotted six months to write rules for evaluating the social and economic impact of proposed projects, but the effect of large and abrupt population increases at the project sites could be disastrous.

Meanwhile, some projects are going forward.

Three pilot plants got help last year in the last gasp of the Department of Energy's synfuels program: a $2.02 billion loan guarantee for the Great Plains coal gasification project in North Dakota; a $400 million purchase agreement for Union Oil's shale project at Parachute Creek, Colo., and a $1.1 billion loan guarantee for the TOSCO Corp. share of the Colony oil shale project near Parachute Creek. The Exxon Corp. is forging ahead there without asking for federal help.

The slowdown, all sides agree, may help the industry in the long run by providing time to do everything right the first time.

"I'm not sure it would have been a good idea to start 10 projects at once," Noble said. "I'd rather do two or three and have them be damn good."