Although some hardly dare believe it, a number of respected energy analysts are taling of an end to U.S. oil imports before the year 2000.

The new statistics are loaded with caveats and often denounced by other reserchers, but even critics agree that import cuts will be drastic enough by the 1990s to at least end U.S. reliance on the Organization of Petroleum Exporting Counties.

The vision of total oil independence is non-ideological, coming both from conservative thinkers like Milton Copulos of the Washington-based Heritage Foundation research group and from more liberal theoreticians such as Henry Kelly, a former associate director of the Department of Energy's Solar Energy Research Institute who is now with the congressional Office of Technology Assessment.Even the Department of Energy sees the 21st century drawning with imports at one-third current levels, without any extraordinary government policy shifts.

The major dissenters are big oil companies like Exxon, whose executives see imports holding roughly steady into the next century, and conservationists who fear that the end of federal help will crippled the energy-saving trend.

Although the vision of an energy self-sufficient nation is by no means guaranteed and far from unanimous, its proponents say it will result from three trends: unprecedened domestic energy conservation, soaring oil drilling rates at home and a domestic fleet of automobiles that gets up to 55 miles per gallon of gasoline. It is the first time that the notion of import independence has been considered without the assumption of a major social transformation.

Energy independence has been a subject of national discussion since the Mideast ol embargo rocked the world economy with a surge in oil prices in 1973. But despite the creation of an Energy Department, then-President Carter's declaration of a "moral equivalent of war" on energy waste and megabombs of political rhetoric, oil imports hit their peak in 1977 at 8.8 million barrels a day, or 6,100 barrels a minute. That was a staggering 48 percent of U.S. oil demand.

President Reagan took office promising to unleash American industry on the problem of energy gluttony, calling it a national security concern and one of his top priorities. One of his first acts was to complete decontrol of oil prices, arguing that it would stimulate production and slow demand.

But by last March, before any change in policy had had time to have effect, oil imports already were down to 5.8 million barrels a day, a reduction of 3 million barrels a day from 1977, lower than anyone had predicted and lower than Carter vowed to achieve by 1985. Overall energy use is down, too, although the economy has grown considerably since the peak import period.

Automobile mileage is going up faster than Detroit argued was possible, and domestic oil production is not falling off as fast as the experts foresaw.

The White House policy office professes not to be surprised by the new reports. "The ranges that any reasonable person is considering include zero (imports) by (the year) 2000," says energy specialist Danny J. Boggs. Administration policy, however, is not airmed at zero imports but at maximizing efficiency and production, he said.

"We're trying for basic energy security, where the economy is not subject to disruption by foreign activity on the oil marked," Boggs said. "Zero imports is not necessarily the goal."

The current world surplus of oil and its dipping price are only temporary jiggles in the OPEC nations' long-term strategy of steady price increases, according to the zero-import view, and are not reflected in the predictions.

"Gasoline use dropped 13 percent last year," says Copulos. "That startled everybody and now all bets are off."

He predicts a 15 percent annual decline in gasoline use over the next four years as 1969 to 1976 models are traded in for higher mileage cars. New technology will wring more gasoline out of every barrel of crude while oil users turn more to different fuels: "The general trend toward consevation has been consistently underrated," Copulos says.

At the same time, the current upsurge in oil well drilling will produce a "very sharp increase" in domestic oil production, Copulos said: "It's even possible that by the end of the decade, or very early in the 1990s, we may find no need for imports. And that's without synthetic fuels." Copulos was named last week to the National Petroleum Council, which advises the secretary of energy on oil matters.

Successful domestic oil drilling in the first quarter of 1981 soared by 35 percent over last year's rate, according to the American Petroleum Institute, largely in developing known reserves. But there were 25 percent more weels in new territory than last year, and the total number of oil and gas wells and dry holes is already at 15,614 -- an increase of 18.7 percent over 1980 figures. If the rate of increase holds steady it will set a record. o

Critics of this viewpoint note that more drilling does not necessarily discover new reserves, that U.S. resources are pretty well known, and that the laws of physics prevent those reserves from being sucked out of the earth much faster than they are already. But all sides acknowledge that U.S. production, which peaked in 1970 at 3.5 billion barrels annually and dropped steadily for six years, has held roughly stable since 1977.

Kelly sees continued hevy conservation as key to an import-free future. "There are a lot of different (energy source) combinations but it's certainly possible to get oil imports down to zero" by the year 2000, he said in an interview. The Reagan administration killed nearly all Department of Energy programs boosting conservation, arguing that price alone is the best incentive. That action will make increased conservation "a lot harder," but not impossible, Kelly said.

His scenario is based on continued energy-saving in old offices and homes: caulking, insultation and storm windows, and new, energy-efficient furnaces, refirgerators and other large appliances. These savings free natural gas for use in industry, displacing oil there, Kelly said. Cuts in electricity consumption reduce utilities' need for the oil burners they switch to during peak demand periods.

Automobiles could be getting 60 miles per gallon by 2000, and if the nation's fleet averaged 55 miles per gallon, 3 million barrels of oil would be saved a day, Kelly said. The major question mark here, according to Colleen Belli of General Motors Technical Center in Warren, Mich., is consumer demand.

Federal regulations will require 1985 autos to get 27.5 mpg, "but demand is well ahead of that," she said: GM cars will average 31 mpg by 1985 and 35 mpg in 1990.

On April 1, DOE projected imports at 5 million barrels daily through 1990, dropping sharply to 2 million in the year 2000 and to 1 million by 2020, largely through price-induced consevation and industrial shifts from oil to coal.

An Amoco Oil Co., chief economist Ted Eck sees late-'90s imports at around 2 million barrels daily, calling that "a comfortable number . . . because you can envision all of it coming from the Western hemisphere." The idea of a 55 mile-per-gallon auto fleet by then is "categorically impossible," and 45 miles per gallon is more reasonable, he said.

Major critics of the low-import scenario include Exxon, which forecasts a return by 1990 to the old peak of 8.8 million barrels a day and a decline to the end of the century to 4.7 million barrels, "depending on the level of synthetic liquid (fuel) production," a spokesman said.

Conservationists also doubt that zero imports can occur with zero federal help for energy savers, because of continuing inflation.

All this assumes no Mideast war or other major international market disruption, no mammoth oil discoveries and no altruism at OPEC. "No one predicted Iran," says Henry Kelly. "Life is never fair to forecasters."