U.S. natural gas prices are expected to rise substantially in the next three years while oil prices continue to decline, which could "result in dramatic increases in imports of oil and oil products," according to an Energy Department forecast released yesterday.

The Energy Information Administration, in releasing its annual energy outlook, said that as industrial users and utilities continue switching from gas to lower-cost oil, imports "could rise from 4.2 million barrels a day in 1982 to as much as 7.6 million barrels a day in 1985."

An increase of this magnitude in U.S. oil imports, coupled with increasing demand from other industrialized countries as a result of the expected economic recovery, would end the petroleum glut of the past 18 months and make possible renewed price hikes by oil producers.

The Energy Department's projection of sharply rising natural gas prices is based on the assumption that there will be no congressional action to change the existing regulatory framework. A Reagan administration proposal to totally deregulate gas and a variety of bills designed to lower gas prices are now before Congress.

EIA Administrator J. Erich Evered told a news conference that his forecasters are not yet able to evaluate the potential impact of these bills on natural gas prices.

But while forecasting a sharp rise in natural gas prices, Evered said that government analysts expected "the recent declines in oil prices to continue for a while." He added that the retail prices of gasoline and home heating oil should "stay within a few cents" of where they now are or perhaps even fall slightly.

These short-term declines in oil and gasoline prices, Evered said, are not expected to result in a shift away from conservation.

The average American household, which currently is consuming energy at "only three-quarters of the level of a decade ago," will continue to reduce the amount of energy it uses in the decade ahead, the EIA predicted.

The report also said:

* Energy consumption in the United States declined in 1982 for the third consecutive year. But whereas declines in previous years primarily resulted from consumer conservation in response to higher prices, the 1982 decline reflected the recession and a relatively warm late fall and early winter.

* The annual per capita consumption of energy in the United States last year fell to 306 million BTUs (British thermal units), the lowest level in 15 years. This compares with a per capita peak of 353 million BTUs at the time of the Arab oil embargo in 1973.

* Net imports of petroleum in 1982 fell to 28 percent of the total oil used in the United States, the lowest level since 1972. Imports from Arab members of OPEC fell to 5.5 percent of total U.S. consumption, compared with 17.3 percent in 1977.