By the time people are ready to uncork this year's Yuletide cheer, a new District of Columbia law should make it easier for suburbanites to evade restrictions against buying liquor in the city and carrying it home.

The new law would severely restrict out-of-state revenue agents from staking out D.C. liquor stores in search of people buying in quantities that are illegal in those other states.

Such buyers are followed out of the District and are arrested and often fined.The liquor is confiscated.

Existing Maryland law prohibits an individual from carrying more than one gallon a month into the state from another jurisdiction. A newly amended Virginia law prohibits carrying more than four liters (slightly more than one gallon) at a time.

With expressed reluctance, Mayor Walter E. Washington has informed the City Council, which passed the new measure in May, that he was letting it go into effect without his signature. it will not be effective until after Congress has an opportunity to decide whether to veto it, a process that may not be completed until the Christmas holiday season.

At present, out-of-state revenue agents can conduct stakeouts without notifying D.C. authorities. The new law would require the agents to register with the D.C. police three days in advance, specifying which stores are to be watched. Agents who fail to register could be fined up to $300.

In a letter to the council, notifying it of his decision, the mayor declared:

"With the exception of bringing increased revenues to (a) few high-volume retailers in the District, this legislation would result in little benefit to the District and its resident . . .

"This legislation will needlessly obstruct legitimate law enforcement activities of other states attempting to control bootleg operations and maintain their tax revenues."

The new measure was proposed last year by the D.C. Liquor Dealers Association, which contended that customers of its members' stores were frequently harassed by the tax agents.

Sponsored by council Chairman Sterling Tucker, the bill was enacted on a unanimous voice vote by the council. Some council members said the new law should increase sales to suburbanites and bring in larger D.C. liquor tax collections.

The mayor's decision to let the measure become law without his signature, rather than vetoing it, reflected political reality. Since it was approved by all 13 council members, it was obvious that a veto would have been overriden.

In his message to the council, the mayor said passage of the bill could backfire, since other states may retailate by reducing their cooperation with the District in law enforcement.

The District is vulnerable to smuggling and bootlegging of cigarettes, the mayor said, since its tax rate is higher than that of its neighbors.

Although Congress could veto the new liquor surveillance bill, it has not overturned a council-passed law since the city home rule charter went into effect in 1975.