The Department of Transportation is considering a policy for National Airport that appears to be little different from a Carter Administration plan rejected by Congress last year, sources said yesterday.

Like the policy advanced by former DOT secretary Neil Goldschmidt, the "new" plan would reduce the number of flights permitted at National, impose an earlier absolute nighttime curfew on flights, cap the number of passengers who could use the airport in the future, allow the use of some wide-bodied jets and extend the socalled perimeter rule that now generally restricts nonstop flights from National to within 650 miles.

Administration sources cautioned yesterday, however, that the latest plan is still subject to significant change. The whole question of a new National Airport policy apparently has sparked a heated debate within the department, with proponents for a continuation of something like the Goldschmidt plan outnumbering opponents to date.

Opposition to the Goldschmidt approach was led by Federal Aviation Administrator J. Lynn Helms, who was said to favor a policy that would reduce the regulatory approach. Helms is said to have favored lifting the cap on the number of daily takeoffs and landings at National and attacking the noise complaints with strict rules to reduce the use of the noisier airplanes.

If the plan being circulated is approved, it is sure to please local community groups that have led the fight against National and is likely to displease members of Congress and the airlines, whose flight schedules would be cut. With the advent of deregulation, the number of airlines seeking to use close-in National already has created an almost impossible job for the airline-scheduling committee that tries to fit airline requests into the available operating limits.

With the government's blessing, the airlines have been working out operating schedules at the airport among themselves since 1968. But last fall, the airlines were unable to achieve agreement on a schedule that would accommodate all the demands -- including New York Air's plans for Washington-to-New York service -- and the government had to step in and allocate the slots, the industry term for takeoffs and landings.

Under the plan circulating in the government now -- but "not set in concrete," a source emphasized -- the number of takeoffs and landings permitted by the airlines would be reduced almost 20 percent, from the current 640 to 522. Besides reducing the number of airline operations from 40 to 36 an hour, the plan also would impose an absolute 9:30 p.m. curfew, a move that would cut out 62 flights now permitted to land or take off after 9:30.

Other elements of the plan could make Eastern Airlines a big winner and New York Air, its low-fare competitor in the Northeast corridor, a loser. The plan would keep intact a provision in the current airport rule that allows airlines to fly unlimited extra sections of flights, a provision used daily by Eastern's Air-Shuttle between Washington and New York. At the same time, the plan would eliminate a loophole in the rule currently used by New York Air to fly more flights than the number of slots it has.

The government apparently would allow jumbo jets into National for the first time if the airlines could show they could be operated safely, a decision Eastern's been seeking for a long time so that it could use its Airbus A300 here.

Sources said the new policy has been sent to the Office of Management and the Budget for review and could be released next week.

The Goldschmidt policy, released last summer, originally was scheduled to take effect on Jan. 5, but its implementation was delayed by Congress until April 26. In February, DOT Secretary Drew Lewis proposed to delay until October the plan he inherited.