A handful of federal workers here who want to work evenings and weekends to make up for time off during the inauguration day holiday have run up against a dusty government Catch-22 regulation. It says one cannot work for Uncle Sam for nothing.

The idea of donating time to the government is not new. Many employees did it on the sly with management cooperation during the two world wars and the Korean conflict. When President Nixon announced Phase 1, some employees tried to refuse pay raises or in-grade salary promotions. During President Ford's WIN (Whip Inflation Now) campaign, many sought to work for nothing. But they also ran afoul of a law passed prior to Abraham Lincoln's administration and now part of 31-U.S. code, sub-section 665B.

As laws do, this one goes on and on, saying in effect that no officer or employee of the U.S. government "shall accept voluntary service."

The rule is flexible enought so that Henry Kissinger was not jailed for burning the midnight oil with the Arabs and Israelis when an eight-hour day would not suffice. Nor does it bar "bona fide" professionals, administrators or supervisors from working after hours without pay. Many of them do so.

But the law, designed to protect rank-and-file employees, does not allow a supervisor to permit subordinates to work for free. The recently enacted Fair Labor Standards Act puts new teeth into antivolunteer statutes.

THe idea of working free for Uncle Sam has been debated by a group of Army civilian employees in Alexandria. They contactauguration day but wanted to make a gesture to the nation and their government, perhaps by working a Saturday to make up for lost time.

When the workers contacted the appropriate authorities they were congratualted on a sweet idea and a nobel gesture. But do not try it, they were told, or somebody is going to come down hard on you or your boss. As with most things, though, there is a way.

You must take money from Uncle Sam for services rendered. But there is no law against giving it back to him via the U.S. Treasury.

In fact, several members of Congress have returned or are now giving back all or part of recent pay raises. Some federal workers also have donated parts of their salary or pay raises to the Treasury.

A surprising number of people name the government in their wills nad, when they die, turn over the cash parts of their estate s to the government. In most cases the gifts are meant to help retire the national debt, which is under no danger of being retired.

Others make gifts to specific programs, such as the National Park Service. People have given dogs to the Border Patrol, material to the Interior Department and paintings to some federal operations.

One advantage of giving money to the Treasury is that it can be considered tax-deductible on the same dollar-for-dollar basis as are donations to charities. Uncle Sam can hardly be classified as a charitable organization, but he certainly comes under the heading of a nonprofit organization.

If you want to send the government a check for the amount of your salary on inauguration day, contact somebody in the Treasury office that handles gifts to the United States. They will take your money.