The long-debated plan to control noise and congestion at National Airport will take effect Dec. 6, Transportation Secretary Drew Lewis announced yesterday. But key measures to limit engine noise will be delayed.

The product of a decade of political battling, the policy is designed to reduce scheduled takeoffs and landings of jet airliners from 40 to 37 per hour, cap passenger volume, now 14.5 million per year, at 16 million, allow new direct service to four major cities and promote the underused Dulles International Airport.

Late-night decibel (loudness) limits on engine noise, considered a key element by many civic groups along the Potomac River, will not be implemented until March 1 to give airlines time to devise new schedules, Lewis said.

In addition, the department will rethink its proposed 1986 implementation date for tighter noise rules that would force airlines to switch to a new generation of quieter jets, Lewis said. Airlines had expressed doubt that they could acquire enough new planes by that date.

Unsettled questions on noise leave room for further debate and changes. But area civic groups and political leaders generally have called Lewis' plan a welcome first step in controlling growth and noise at the busy airport, where scheduled jets first landed in 1966.

"It meets most of the goals that I and other members of the local congressional delegation had established," said Sen. John Warner (R-Va.), who coordinated support for the policy in the Senate. Warner said he was discouraged that the night-time limits will be delayed by three months.

Eric Bernthal, president of the Coalition on Airport Problems, which links civic organizations concerned about National, described himself as "a little angry" over the delay on night noise standards. "Without that, there's no curfew at all," he said.

Currently, there are no noise limits. Airlines are not allowed to schedule flights between 10 p.m. and 7 a.m., but no action is taken against them if their planes actually take off or land between those hours, as happens routinely.

Nighttime rules originally included in Lewis' airport plan established decibel limits that Federal Aviation Administration officials said would stop jet traffic after 10:30 p.m.

Daytime noise limits, first intended to take effect with the rest of the plan, also will be postponed pending further study, Lewis said. The rules were not intended to alter exist-ing daytime traffic but to keep out noisier planes. However, at least one airline has said its planes might not meet the limit.

Carriers and aircraft manufacturers also questioned whether there would be sufficient plant capacity and money to give airlines calling at National enough of the new quiet jets by 1986. In response, the Transportation Department is restudying that date, Lewis said.

Takeoff and landing "slots" remain as originally planned -- 37 per hour for scheduled air carriers, 11 per hour for smaller, mostly prop-driven commuter planes and 12 per hour for "general aviation," a category that includes corporate and private planes. Airlines still could exceed their slot allocations if passenger levels demanded it.

FAA officials point out that, for the present, questions of flight reductions under this formula are academic -- the air traffic controllers' strike has already reduced traffic by 20 to 25 percent, far more than the plan could accomplish. Officials estimate it might reduce traffic by 5 to 10 percent from prestrike levels.

The plan also will accelerate construction of access roads to Dulles International and give consideration to subsidizing bus or limousine service there from downtown.

National Airport's "perimeter" for nonstop service will be expanded to 1,000 miles, allowing nonstop service to four additional major cities: Birmingham, Fort Lauderdale, New Orleans and Kansas City. The current 650-mile perimeter excludes those cities.

Last year, Congress killed a Carter administration attempt to establish an airport policy. This year, after intense lobbying by Secretary Lewis and area legislators and a deal to defuse airline objections to the plan, congressional objections were dropped.