The Department of Transportation's proposed new plan to limit the number of flights at Washington's National Airport has run into opposition at the Office of Management and Budget, sources said yesterday.

The Reagan administration's top regulatory review official, James C. Millier III, OMB's administrator for information and regulatory affairs and staff director of the President's Task Force on Regulatory Relief, is said to have raised objections to the proposal on the grounds that it would add to the federal regulatory burden rather than reduce it.

Although not all the details of the DOT proposal were available, sources said highlights of the National Airport policy sent to OMB include:

A reduction in the number of takeoffs and landings permitted by the commercial airlines from the current 40 to 38 an hour and a limit on the number of passengers who could use the airport in the future.

A 350-mile extension of the so-called perimeter rule that now generally restricts nonstop flights from National to within 650 miles of the city.

The closing of two loopholes used extensively by airlines flying in the Northeast Corridor. One, used daily by Eastern Airlines' Air-Shuttle between Washington and New York, allows airlines to fly unlimited extra sections of flights. The extra sections are not counted against the airline's allocation of slots -- the industry term for takeoffs and landings.

The other loophole, used by New York Air, Eastern's low-fare competitor, allows airlines to fly more flights than the number of slots it has, as long as good weather and so-called visual-flight rules prevail. This loophole is also used extensively by commuters and pilots in private planes. Removal of both loopholes would require the two airlines to either increase their current slots or curtail some service.

A number of provisions seeking to make the use of Dulles International Airport more attractive to the airlines and their passengers. These would include raising the fees for landing planes at National, accelerating the construction of a 2 1/2-mile road extending the Dulles Access Road eastward to connect with I-66 and creation of a downtown bus terminal where passengers could board free buses to Dulles.

Transportation Secretary Drew Lewis met Monday with Miller, who said he would favor a plan that moved in the direction of deregulation and imposed fewer regulations than the one drawn up by DOT, according to informed sources.

A spokesperson for DOT said yesterday the National Airport policy would be released next week but declined to comment on any details of the plan. w

If the DOT plan is released as it is now drawn, it is likely to face some opposition from Congress, which rejected a similar flight-reduction plan proposed last year by former DOT Secretary Neil Goldschmidt. The National Airport policy has plagued federal transportation policy makers for years.

If Congress doesn't overturn the plan, its imposition is likely to result in further DOT involvement in the airline scheduling process for National.