The Department of Transportation plans to propose steps likely to lower the annual passenger limit at National Airport while allowing two additional takeoffs or landings by commuter planes each hour, aviation sources said yesterday.

The proposal will be published in Tuesday's Federal Register, sources said, provided it is approved by the Office of Management and Budget, which received it for review late in the week.

The current annual passenger cap at National is 16 million, about 2.5 million above the actual figure. Sources said the proposed change, being pushed by recently appointed Transportation Secretary Elizabeth Dole, would drop the cap to 14.8 million or to the number of people using the airport in 1984, whichever is higher. In no case would it be higher than 16 million under the plan.

Planners expect traffic to keep rising slowly but to stay below 15 million in that period. If that happens, Dole's plan would result in a lowering of the limit. The plan would be a victory for civic groups that have fought for reduction in traffic at the airport and a shift to underused Dulles International Airport.

But before being implemented, it would be subject to public comment and lobbying and would be hotly contested by the airlines, which have major investments in terminal facilities at National and who view a lower limit as unfair restriction on their operations, industry sources said.

Transportation Department spokesman Tom Blank declined to comment on the reported changes in the cap and commuter quotas. "The secretary has made no final decision on any changes to the metropolitan Washington airports policy," he said.

The other major aspect of Dole's proposed revision, sources said, is to allow two more "operations"--takeoffs or landings--by certain types of propeller commuter planes that can use National's "stub runways," the end portion of National's shorter runways beyond the intersections with the main runway.

Currently, 11 commuter plane takeoffs or landings are allowed per hour. Commuter lines have argued that since their planes can land on the stubs without interfering with jet traffic on the larger runway they should get more access to the airport.

OMB director David Stockman has in the past proposed that the free airport landing rights be auctioned off, an idea rejected by former Transportation Secretary Drew Lewis. Sources said that in the plan review, OMB might push Dole for some sale of the rights. The proposals come as the Federal Aviation Administration is considering an Eastern Airlines request to allow its new Boeing 757 jets to use National, which is opposed by community groups.