Senate and House conferees agreed yesterday to block action for 60 days on a controversial plan to reduce the number of passengers using National Airport.

The compromise, worked out by key House and Senate members, was aimed at providing Transportation Secretary Elizabeth Hanford Dole additional time to seek a new accord with airline and other officials.

Under current rules, a maximum of 16 million passengers is allowed to use National annually. Dole has proposed reducing this ceiling to 14.8 million passengers a year. The suggested shift would not lead to immediate cutbacks in service at National, which now handles 13.5 million passengers annually, but is aimed at curbing expansion after 1985.

Advocates of Dole's plan, including Washington-area members of Congress and some civic groups, have argued that it would encourage increased airline service at Dulles and Baltimore-Washington international airports, which long have been regarded as underused. The airline industry has fought moves to impose new restrictions at National, and many members of Congress also have objected to possible reductions in service at National.

Yesterday's agreement ended a deadlock between the House and Senate over the issue. The House had voted to block Dole's plan, but the Senate later rejected the House proposal. The new measure is expected to gain final House and Senate approval soon.

While noting that the proposed 14.8 million cap "may well be appropriate," the conferees urged Dole to reconsider the method by which the ceiling on passengers is set. They suggested, for example, that passengers on shuttle, commuter or connecting flights might be exempted from the ceiling.

A spokesman for Dole said she was "very pleased" that Congress had not blocked her from considering a change in the ceiling.

A spokesman for the Air Transport Association, an airline industry group that opposed the 14.8 million passenger limit, said yesterday that he had no immediate comment on the congressional compromise. Rep. Frank R. Wolf (R-Va.), who has favored the lower ceiling, hailed the agreement as a "significant step forward."

The ceiling on passengers using National was included in a $10.9 billion appropriation bill for transportation programs that the conference committee approved yesterday. In an attempt to head off a possible veto by President Reagan, the committee reduced outlays, chiefly by cutting Federal Aviation Administration allocations by about $300 million.

The bill also provided a rebuff to the Reagan administration's attempts to reduce and eventually eliminate federal operating subsidies for mass transit, including Washington's Metro system. The measure provides $873 million for operating subsidies next year. The administration had proposed cutting operating aid to $275 million.