Federal workers may get a peek today at a very special Christmas present from President Carter.

If the gift is what civil servants hope, it will be official word that the president has decided to give them the day off on Monday, Dec. 24. That is the day before Christmas. He may link it with a national day of prayer for the American Hostages in Iran.

The gift would amount to a $25 million day off with pay for area civil servants who make up most of the adult work force. It could be a boon to merchants too.

Some advice: Don't make any vacation plans yet. And do not flood the White House switchboard, either asking for or demanding the day off. It is not official until the president says so. And he does not have to grant the day off either by law, custom or to win reelection.

Insiders say the president is very aware of the calendar quirk that puts Christmas on a Tuesday. He knows about the energy savings to government if federal offices could be kept closed Saturday, Sunday, Monday and Tuesday. And of the goodwill it would generate from the bureaucracy.

People who have been attempting to read the crystal ball on the subject predict that Carter will okay the special day off -- and that he will do it this week. Maybe today.

Most private industry workers probably will not benefit from the extra day off, although it could nudge some bosses -- especially in smaller offices -- to follow Uncle Sam's suit. But the decision to give federal workers the day off before Christmas could -- when and if it comes -- be a big financial boost to area merchants who do most of their business with the nearly 400,000 civil servants here.

The extra day off -- if it comes -- could also benefit many of the 60,000-plus military personnel stationed here. Many of them work alongside civilians and, for energy-saving purposes, it wouldn't make sense to keep them on the job when their civilian colleagues get the day off.

There is some question as to what the U.S. Postal Service would do if other federal workers get an extra day off. This is their peak time of year, and Monday an especially important mail-moving day. District government offices could be expected to follow the president's lead -- but that, too, is speculation.