The Department of Transportation yesterday backed away from its plan to permit airlines to use wide-bodied jet aircraft at Washington's National Airport, at least until next April.

Introduction of the quieter, more efficient three-engine jumbo jets at National was one element of an over-all plicy devised for National by DOT and scheduled for implementation on Jan. 5, 1981. But DOT officials said yesterday that since Congress delayed until April 26 their proposed cuts in the number of flights at National, it wouldn't go ahead with any of the policy until then.

"Our policy was a package that resulted from a conscientious effort to balance the needs of air travelers with the airport's neighbors' demonstrated need for noise relief," DOT General Counsel Thomas G. Allison said yesterday. "It must be implemented as a package."

Another element of the policy that will be put off would have made it possible for cities within 1,000 miles of Washington -- like New Orleans and Kansas City -- to receive nonstop service to and from National. The limit, with some exceptions, is now 650 miles. Another part of the proposed policy would have limited passenger traffic at National to 17 million a year; traffic this year already ahs surpassed the 15 million mark.

Allison, flanked by Virginia Reps. Joseph L. Fisher and Herb Harris, made his remarks at a news conference at National Airport. The two Democratic congressmen, whose districts adjoin National, supported the DOT position even though it delays the use of some quieter airplanes. "Wide-body jets and longer nonstop flights must not be allowed into National until we've secured a significant reduction in total jet operations and have in place a tight, enforceable curfew on night flights," Harris said.

Fisher added that those living near the airport are concerned about the total number of flights and that implementing part of the policy would reduce the pressure for imposing reductons on the number of operations permitted at the airport each day.

DOT had hoped to reduce the number of major commercial jet flights at National by about 20 percent in January by cutting the number of hourly flights from 40 to 36 and imposing an earlier evening curfew at the airport. Last month, however, Congress barred DOT from reducing the number of flights at National until April 26, the first day of Daylight Savings Time when airlines generally make major schedule changes.

Besides delaying implementation of its National Airport policy, DOT yesterday put out for public comment three alternatives systems it is considering for allocating the limited access to the airport among the increasing number of airlines wanting to use it.

Allocations for slots -- the industry term for the number of takeoffs and landings permitted at the airport -- have been worked out for the past 12 years by the airlines themselves with the government's blessing. But the task has proven increasingly difficult as opportunities for new routes and the creation of new airlines expanded under airline deregulation at the popular and convenient airport.

Yesterday, DOT said it was considering three plans for allocating slots, which it described in complicated detail in 66 pages: an administrative allocation formula, under which DOT would make decisions using various criteria after considering airline requests; an auction system, under which airlines would bid for the use of National facilities, with special consideration for small and medium-sized airlines; and a continuation, with some changes, of the current airline scheduling committee procedure.

The plans are being considered for use after April 26.