The Defense Department and the Central Intelligence Agency engage in wholesale evasion of White House orders aimed at more open government.

This is the essence of a report by the General Accounting Office to be released today.

The GAO, an investigating arm of Congress, discloses that the Pentagon counted 3.6 million messages it classified in 1977. But one Pentagon unit alone, the National Security Agency, acknowledged that it had stamped as secret from 50 million to 100 million messages -- at least more than 13 times the reported total.

In the same year, the CIA reported it had classified or declassified 587,000 documents. The GAO cited an agency acknowledgement that the total two years earlier was in "the neighborhood" of 5 million.

All departments of government combined told a White House interagency committee they had made 4.5 million decisions to classify in 1977. The actual number, says the GAO, "is not known" but "could range from 70 million to 100 million or higher."

The congressional accountants conclude that presidential orders to cut back on the misuse of secrecy stamps "have been ineffective." Executive branch watchdogs in charge "did not enforce" their own orders, failed to check closely and "received poor cooperation from some agencies." The GAO notes one problem is that the White House monitors include representatives from the agencies that most frequently breach the rules.

But with characteristic caution, the GAO makes no judgment on whether the government is abusing its power to classify.

Sen. William Proxmire (D-Wis.), however, charged in a statement that the study reveals "massive overclassification of national security documents and flagrant noncompliance by the Pentagon and other agencies wity procedures set up to prevent abuses of the classification system." Proxmire is chairman of a Joint Economic subcommittee that requested the GAO study.

The first presidential order to curb abuse of classification was issued by Richard M. Nixon in 1972. It instructed all agencies to review and count their use of "secrecy" stamps and, with few exceptions, make public all classified government papers in six to 10 years.

President Carter, contending there was still too much secrecy in government, issued a new order last year to declassify most papers in six years.

The GAO, however, reported that the Carter order, as interpreted by the agencies, actually may have increased secrecy by expanding the number of those with power to wield the classification stamp.

The GAO discloses that the White House interagency group overseeing the program misled Congress and the public in its 1977 report.

That document asserts that 80 percent of the papers studied for classification were placed in a category that ultimately would open them to the public. But this box score left out the Pentagon, the Energy Department and the CIA. Between them, they account for 97 percent of the secrecy stamps, and the "overwhelming majority" of their decisions put papers in "exemption" categories -- not for public disclosure.

For the most part, the Pentagon defended its failure to count and index classified documents on the grounds that it would take too much time and cost too much. The Pentagon said it had made a study of indexing and concluded it would cost $20 million to $50 million. GAO asked to see this report and was told it could not be found.

An unnamed Army commander quoted in the GAO report said he had not bothered to collect required statistics and, "by not doing so, we achieve a significant cost avoidance."

Both Presidential orders call for reducing the number or officials allowed to use "secrecy" stamps to curb misuse. A zealous National Security Agency complied by empowering only two persons to classify the tens of millions of documents it marks "secret" each year.

However, the Nixon order was evaded by the Pentagon and others who set up "guidelines" so that thousands of bureaucrats could classify without specific authorization.

The Carter order specifically approves the "guidelines" technique. According to Proxmire, this means "virtually anvone in the Pentagon with security clearance can classify information... clerks and stenographers...."

A Defense Department rebuttal by David O. Cooke, a deputy assistant secretary, says that the GAO study "does not present in accurate perspective a realistic picture" and is "not fully sensitive" to the Pentagon's efforts. He does not quarrel with any of the statistics.

Proxmire concluded that the "executive orders have not been effective" and urged legislation be enacted to "bring the classification problem under control."