High prices and conservation efforts will cure future U.S. energy growth, but demand still will outstrip supply through 1990 unless the nation's basic energy policies are changed, the Energy Department said yesterday.

A new analysis by the department's Energy Information Administration predicted a sharp increase in oil imports, said auto makers are unlikely to meet the fuel economy levels required by law and forecast a substantial growth in the use of nuclear power.

It also said domestic oil and natural gas production, aided by new supplies from Alaska and from offshore areas, will at best hold steady through 1990 and at worst fall about 25 percent below present levels. President Carter's goal of doubling coal production by 1985 will be met five years late, it said.

The department's report to Congress - less pessimistic than the Central Intelligence Agency forecast released last year by President Carter, but more gloomy than some other recent projections - said a world oil shortage appears inevitable sometime in the 1980s.

Energy Information Administrator Lincoln Moses stressed the many uncertainties in his agency's report, saying in a preface: "There are not facts about the future . . . for everyday affairs, not governed by well understood physical laws."

Moses told a news conference one uncertainty is that the report fails to reflect programs proposed in the Carter energy plan, which Congress has been considering for more than a year. Other officials said the report, required by law, had been delayed as long as possible in hopes of congressional action.

"If Congress comes up with an energy package, then the results will differ from our projections," Moses said. "The work is not wasted, however, because we will need a benchmark against which to measure our progress" from any future policy changes.

Rep. Al Ullman (D-Ore.), chairman of the House Ways and Means Committee told an energy policy conference yesterday it will probably be another few months before the energy bill can be passed.

And then, Ullman added, the conference committee that has been wrestling with the package since last year may send only four of its five major segments to a vote in the House and Senate, holding back President Carter's proposal of a new wellhead tax on U.S. oil production.

But Ullman said he still hopes "we can get Congress turned around" and eventually win enactment of the crude oil tax as well.

Ullman spoke at a conference sponsored by the Georgetown University Center for Strategic and International Studies, which was also addresses by former secretary of state Henry A. Kissinger.