Most federal workers stand a good chance of getting a half-day bonus holiday Dec. 24, the day before Christmas, if President Reagan follows past practice.

Although nothing is official until the White House says so, there is good reason to believe that federal (but not postal) employes may get a special Christmas bonus in the form of extra time off. Postal workers probably can forget about any pre-Christmas early release.

Last year, when Christmas fell on a Thursday, the president issued an executive order giving most federal workers the next day off. The U.S. Postal Service, however, kept its 800,000 troops on the job that Friday to process and deliver holiday mail.

This is what has happened in previous years when Christmas fell on a Friday as it does this year:

In 1981, Reagan authorized federal agencies to allow nonessential employes to leave three hours early on the day before Christmas.

In December 1970, President Nixon gave federal workers a half-day off on the day before Christmas.

In December 1964, President Johnson rejected suggestions that federal workers get off early on Christmas Eve.

The decision to release federal employes early sounds simple but isn't, especially in the Washington area.

Turning 350,000 people out on the streets before normal quitting time can be a bonanza for merchants who pick up last-minute shopping business. But the early release can be a nightmare for police, traffic and transportation planners.

The early release creates two rush hours, the first for lucky federal workers who go home early and the second for those unhappy souls (government and private sector) whose bosses say they can't be spared.

If the White House decides on the early release, it has to be careful how it words it. If, for example, the president slips up and declares it as a half-day "holiday," that means employes who have to work must be paid double time. Usually the White House grants administrative leave and allows agency heads to keep essential employes on the job.

Budget News

It now appears that white-collar federal workers will get a 2 percent raise in January, and that federal, military and Social Security retirees will get a 4.2 percent cost-of-living adjustment next month. Senate-House budget conferees have apparently agreed to leave the pay and pension increases untouched, although it is still undecided what to do about raises for government executives.

The compromise budget plan also rejects earlier money-saving proposals from the White House to cut in half lump-sum pension payments to federal retirees and to freeze within-grade pay raises for white-collar workers.

Instead, budget cuts will come -- assuming the budget plan holds up -- from the U.S. Postal Service, which would be forced to come up with major savings without any additional increase in postal rates.

The budget won't be final until Congress signs off on it and the president signs it. But the pay raises appear safe, as do lump-sum payments and within-grade raises.