Because of their relatively high salaries-averaging more than $30,000 a year-and large numbers, the more than 340,000 federal workers here are a natural target for sales people and fund raisers.

The latest group to attempt to tap the Civil Service source is the Moral Majority. Some feds who have received brochures and fund-raising appeals from the Lynchburg, Va., organization headed by the Rev. Jerry Falwell want to know how they got on the mailing list.

Anybody willing to spend about $50 can get an excellent mailing list with names, office telephone numbers, room numbers and addresses of thousands of civil servants. The Government Printing Office sells telephone books for the Pentagon, Departments of Energy, Health and Human Services, Education and State, as well as telephone books for the National Aeronautics and Space Administration, National Institutes of Health and the House and Senate.

This week federal workers in half a dozen agencies complained about anti-abortion literature addressed to them at the office from the Moral Majority. Three callers supplied brochures sent to them at the Labor Department, Government Printing Office and Commerce Department. The others refused to identify their agencies, saying they were afraid their bosses had supplied the lists.

Some employes are offended by the appeal; others just don't like being solicited on the job by a group closely identified with the Reagan administration.

Attempts to find out where the Moral Majority got the federal workers names and office addresses flopped yesterday. A spokeswoman in Lynchburg said she had no idea where the mailing lists came from. Officials of the firm that does the mailing for the group did not return my telephone call.

The mailings are not illegal. But some agencies take a dim view of employes getting personal mail -- or being solicited for funds -- at the office.

After getting a ruling from the U.S. Postal Service in 1981, the Veterans Administraton -- one of the biggest agencies in town -- decided that it would deliver personal mail to employes at the office but it would at the same time urge them to give correspondents their home addresses.

VA officials said yesterday that they have also exercised their option to refuse to distribute mass mailings from advertisers, and have sent them back. They said they had no complaints from employes about mailings from the Moral Majority or any other group.

Employes who get mail at the office can tell their agencies to refuse to accept it. Or they can do so themselves. Workers who get any political mailings -- appeals for funds from any political party -- can take it up with the Federal Election Commission or the Justice Department.