Congress received two warnings yesterday of consumer hardship that would result if the administration imposes on import duty on foreign oil.

President Carter's energy and fiscal advisers have suggested that if Congress fails to pass his proposed tax on domestic crude oil to raise prices and deter consumption, he might try to achieve the same result by imposing a $5-per-barrel duty on oil imports.

Sen. Howard M. Metzenbaum (D-Ohio), who opposes both import duties and the crude oil tax requested a report from the Congressional Research Service, which said a $5-per-barrel import duty could add 1.5, to 2.6 percent to the rate of inflation in the year it was inclosed and could, under the worst conditionsf give $33.8 billion a year to the Treasury and petroleum products industry.

Metzenbaum said higher prices would not reduce oil and gasoline consumption, as the experience of the past few years has proved. What is necessary, he said, is mandatory action such as a ban on sale of gas guzzling cars. He induced the Senate to pass such a bill, which is still at issue in a House-Senate energy conference.

The New England Congressional Caucus also released a report by its economics office which said that a $5-per-barrel import fee imposed in three annual steps would raise the cost of home heating oil to New England consumers by 10 percent. The six-state region depends on imported oil for 64 percent of its energy requirements. It is largely beyond the end of the natural gas pipeline.

The bill for the average New England homeowner heating with oil would go up about $20 the fist year and more than $60 a year after the import fee were fully effective, the report said.

An import fee on oil without an equivalent price increase in natural gas wuold widen the price gap between these two home heating fuels, the report pointed out.

Some of the House-Senate energy conferees resumed closed door meetings yesterday to try again to reach agreement on natural gas pricing.

Before the Easter recess, House and Senate conferees agreed on gradual lifting of price controls on newly discovered natural gas. But important differences remain on such issues as the definition of new gas that would qualify for a higher price each year during the transition. Sen. Henry M. Jackson (D-Wash.) said he hoped agreement could be reached next week.

Meanwhile, the White House announced yesterday that Carter will deliver a "major address" next week on energy, inflation and the dollar - presumably to announce his new anti-inflation program.

Administration sources said the talk probably would be Tuesday at a meeting of the American Society of Newspaper Editors here.

Carter told a reception for union members yesterday that "the inflation rate is creeping up" and "unless we all stand firm, cut out waste and have a sound economy . . . we are all going to be robbed of the improvements we made. We are going to have to do something about inflation."