In yesterday's editions, The Washington Post incorrectly reported the amount the Defense Department is spending on films this year. The department is spending $458.2 million on "audio-visual activities," which includes films.

Defense Secretary Caspar W. Weinberger has ordered a 10 percent reduction in what the Pentagon spends on films and publications, but the Pentagon can't tell you what that means in dollars. It knows its films will cost $458.2 million this year, and that there were 647 publications in 1979, the last time somebody counted. Nobody knows how much they cost.

Nor does anybody know how many publications come from the Agriculture Department. Some are produced independently by regional offices, while others are parts of specific programs and are not counted as publications. The annual printing bill is about $25 million, but three-fifths of that is for forms. "If you're going to come up with a figure [for publications] that would include the salaries of people doing the work, you would shortly encompass a great deal of what USDA does . . .," said spokesman Claude Gifford.

When Transportation Secretary Drew Lewis took a look his agency's publications and films, he found that some of them extol the virtues of programs that no longer have virtues. For example, Lewis scrubbed an ad campaign urging compliance with the 55-mile-per-hour speed limit after President Reagan opposed the federal limit during the campaign. The claimed savings: $44,000.

Executive branch agencies have been making discoveries like these since April, when Edwin Harper, deputy director of the Office of Management and Budget, gathered the White House press corps about him and poked fun at such government-produced films and pamphlets as "Dried Flower Arranging."

Taxpayers, he said, were angered that the government spends money on such things and President Reagan was directing a full-fledged assault on the problem. Harper declared that no new films and publications would be permitted until agencies studied their public relations programs and told OMB how they could be cut. He gave them until July 15 to do so, after which OMB will decide what to do next.

The Reagan administration thus became at least the third to try to get a handle on the filmmaking and publications operations of the federal bureaucracy. It is not going to be easy, despite and detailed instructions to the departments found in OMB Bulletin 81-16, "Elimination of Wasteful Spending on Government Periodicals, Pamphlets, and Audiovisual Products." s

Each department and agency sems to be reading the 12 pages of instructions and attachments a bit differently, and there is plenty of latitude for an accomplished bureaucrat to protect his pamphlet. No specific cost-cutting goals have been set and agency heads are authorized to exempt specific publications from the oratorium. In general, it appears that departments have taken the instructions to mean that work already in progress can continue, but that new projects will have to be justified.

No one really knows how much the government spends on films and publications. "We do not have good figures, and that is serious," said Robin Raborn, deputy assistant director for public affairs at OMB. Public affairs offices, she said, "have been unduly criticized as being the main source of the problem. The problem is shared by a number of offices."

The publications and films often raise tough questions. Agriculture has a publication entitled "List of Available Publications." If you need to know how to control bed bugs, Agriculture Publication 683-80 ("How To Control Bed Bugs") will be of some help, but only if you know it exists. Consult the list. Whether it is government's business to tell you how to control bed bugs and to provide a list that tells you where to find help is another matter.

Many government offices produce material for their employes, just as businesses do. "Soldiers," for example, is the official magazine of the U.S. Army. This month, it includes articles such as "Salute: Do I Have To?" and "When You Break the Law," a guide for Gi''s who find themselves in trouble with civilian police.

Should "Soldiers" be eliminated? "It isn't fair to refer to internal publications as public relations because they are for the morale and welfare" of the troops, Department of Defense spokesman John C. Becher said.

The Pentagon also is not including in its review the $112 million it spends on recruiting advertising, most of which is filmed or published, and training films, some of which gave commander-in-chief Ronald Reagan a job during World War II.

Pamela Bailey, of Health and Human Services, said that "a number of educational and communication programs are mandated by Congress" when it establishes a research program and then directs the department to share the information with the public -- for example, a layman's pamphlet on heart disease. "We don't want anyone to get the impression we're trying to cut them back; we just want to make them effective," she said.

Several officials emphasized that they are using themoratorium as much to study ways to improve control over budgets as to find specific projects to kill.

"We haven't actually killed anything," said Bailey.

That doesn't mean you won't, does it?

"It doesn't mean we will," she said.