Transportation Secretary Drew Lewis is expected to unveil a new National Airport policy today that will reduce the number of flights allowed there, end all commercial flights after 10:30 p.m., and virtually ban wide-bodied jets from the crowded, near-downtown airport, according to congressional and administration sources.

The plan also encourages greater use of Dulles International Airport, by accelerating construction of a connector road between the Dulles Access Road and new sections of I-66, and initiating low-cost or possibly free bus service between Dulles and downtown Washington.

Although details were still being developed last night, and affected airlines and industry representatives were still lobbying for relaxing some of the proposals, other highlights of the Lewis plan reportedly include:

Placing a limit on the number of National Airport passengers at 16 million a year, 1 million less than proposed by the Carter administration. Current passenger levels there are running at just above 14.5 million a year, but before an airline slump last year, the annual rate had reached 15.3 million.

Imposing an absolute 10:30 p.m. curfew on landings and departures. The two dozen airlines that now use National must schedule their flights between 7 a.m. and 10 p.m., but because 22 flights are scheduled right at 10 p.m., 20 or so typically land after the curfew. During bad weather up to a half-dozen arrive after 11 p.m.

Decreasing from 40 to 38 or 36 the hourly takeoffs and landings by scheduled airlines. A proposal to require added sections of flights to be counted against the total number of permitted flights was scrapped, reportedly because of intense lobbying by Eastern Airlines, whose hourly shuttle service to New York often adds 20 sections a day.

Extending from 650 to 1,000 miles the distance within which nonstop flights to and from National may be scheduled. This proposal would have the effect of adding nonstop trips to New Orleans, Fort Lauderdale, Birmingham and Kansas City, in addition to encompassing seven cities -- Miami, Orlando, Tampa, West Palm Beach, Memphis, St. Louis and Minneapolis -- that now are exempted from the 650-mile limit.

The new rules would not allow nonstop service to Dallas and Houston, which recently began being served by flights that originate or end at National, but make a stop at Dulles to get around the current regulation.

One congressional source said yesterday the regulation-heavy plan "flies in the face of Reagan's free-skies, free-enterprise philosophy. Such a major change of position, in the face of airline lobbying, is the first signal that the Reagan administration recognizes that National Airport is a political issue."

By coming down on the side of Washington-area interests, the source said, the administration will shore up support for Northern Virginia's two Republican representatives, Frank Wolf and Stanford E. Parris, who captured House seats last November that had been held by Democrats since 1974.

National and Dulles are operated by the Federal Aviation Administration, the only two airports in the nation under the control of the federal government. The agency has been under a federal court order to produce a policy statement for National -- a ruling that results from a lawsuit that argues that overuse of the airport violates various federal environmental regulations.

The final National plan also is said to include rigid noise controls, which FAA Administrator J. Lynn Helms has advocated as a way to reducing citizen complaints, rather than limiting the number of planes using the airport.

But Helms' plea to lift the ceiling on the number of daily flights apparently was overruled by Lewis, who according to one source, lives in the Watergate Apartments under the flight path to National, and has been lobbied by his wife and neighbors to cut down on the air traffic over their apartments.

Parris and Wolf, who have lobbied the White House for tough controls at National, applauded the decision.

Wolf, who with Sens. John Warner (R-Va.) and Charles McC. Mathias (R-Md.) was briefed at a breakfast with Lewis last week, said: "From what I know, it addresses both over-crowding at National and underutilization at Dulles. It's an important step forward. I'm pleased the administration and Secretary Lewis have listened, and responded, to the needs of the Washington metropolitan area."

Paris agreed. "As I understand the thrust, it imposes just exactly the kind of goals we've been working for. I couldn't be happier."

Wolf said that while some of the passenger traffic will be diverted to Baltimore-Washington International, he believes most of it will go to Dulles, especially if quick, low-cost ground transportation is provided to the airport, about 20 miles west of Washington.

The Carter administration plan, advanced by then-DOT secretary Neil Goldschmidt, also sought to reduce congestion and noise at National, but its implementation was grounded by Congress, many of whose members commute via National and zealously have opposed any attempt to cut down on the number of flights there.

The plan Lewis will announce will not require congressional approval, although Congress has the power to intercede in the matter.