Following the old advice on how to catch a thief, the Reagan administration set out a public relations not yesterday in the hopes of killing off some public relations efforts it doesn't support.

The effort comes under the heading of the attack on the dragons of "waste, fraud and abuse," and it is developing into a weekly serial in the White House briefing room, starring Ed Harper, deputy director of the Office of Management and Budget, who is playing St. George to the triple-headed dragon.

Yesterday, the dragon was found lurking in a maze of government audiovisual aids and publications.

President Reagan ordered a moratorium on production of new audiovisual materials and publications and a review of existing ones. "The federal government is spending too much money on public relations, publicity and advertising. Much of this waste consists of unnecessary and expensive films, magazines and pamphlets," the president said in a statement released by his press office.

To illustrate this complaint, Harper brought his one-man, low-budget show before reporters in an effort to capture a little free publicity, courtesy of the television networks, newspapers and radio broadcasting companies that keep representatives lurking in the White House press room.

The title of this week's episode, according to the handmade poster Harper held up, was: "Flics and Flacs." More than $100 million could be saved annually by cutting back on government-made flicks. Additional untold millions of what are never called simply "dollars" at such sessions, but always "taxpayers' dollars," could be saved by eliminating flacks -- public relations types -- and unnecessary government publications, Harper said.

At one point Harper said the savings could add up to billions, but he backed off and suggested that his questioners await July 15, the date the president has set for completed reports from all departments on how to eliminate superfluous flicks and flacks.

Harper explained that one of the problems Reagan budget-cutters face when they ride out to do battle with public relations is that expenditures for publicity are well-concealed in the thicket of budget numbers.

Harper sought to slay the dragons with ridicule. The Education Department, he reported, had spent $68 million over six years to make films under a mandate to ease "minority group isolation resulting from desegration."

Some of the films won prizes, but they strayed far from the original goal of the program and the department spent an additional $500,000 to hire a public relations firm to get its films on TV, Harper said.

The Defense Department made two markedly similar films on espionage at roughly the same time, Harper added. But he praised the Pentagon for having undertaken a review of its publications in 1972 and 1973 that resulted in a total of 1,402 periodicals being slashed to 647.

Government publications titled "Dry Flower Arranging," and "Organic Gardening: Think Mulch," attracted Harper's ridicule. He also raised the question whether the government should be in the business of publishing guides to buying a new car and to rust, as in "Automotive Rust: Its Causes and Prevention."

Harper's text last week -- an appeal to federal employes to report waste and fraud wherever they found it -- might have been titled: "Whistle-Blowing: A Beginner's Guide." His presentation included a list of already established hotline numbers for whistle-blowers to call, and a guarantee that the administration will stand by whistle-blowers to protect them from reprisals.

Next week? An aide to Harper said the topic has not yet been chosen, but the show will go on.