The Carter administration's plans for handling classified information were assailed yesterday as a backward step that would breed more secrecy than the system established by President Nixon.

In a sharply worded critique delivered to the White House Office of Management and Budget, nine national organizations, including the American Civil Liberties Union, Common Cause and Ralph Nader's Public Citizen Litigation Group, attacked a proposed executive order drafted for the President's signature as "particularly disappointing " in view of Carter's professed commitment to an open administration.

The chairman of the House Government Information Subcommittee, Rep. Richardson Preyer (D-N.C.), delivered a separate complaint, saying that the proposed decree is "weighted towards secrecy" and "notably deficient in detecting and correcting abuses" of the classification system.

Preyer said, among other things, that the proposal would not result in a significant reduction in the thousands of government officials with authority to stamp documents "Top Secret," "Secret" or "Confidential."

The Carter proposal, made public last month, was the result of the President's request to his staff last June to review the government's entire secrecy system. Yesterday was the deadline for comment by interested parties. Once signed, the order would place secrecy rules promulgated by Nixon in 1972.

Both the ACLU and Preyer took special exception to a draft provision of the Carter plan that would require development of a uniform "secrecy areement," which any government agency with classification authority could impose of its employees as "a precondition of access to classified information."

The Central Intelligence Agency has long had such a rule, and has effectively used it to censor the writings of one former employee, Victor Marchetti.

Preyer called this provision "singularly objectionable." He protested that the use of such a procedure government-wide would have "a distinctly 'chilling effect' on potential 'whistle blowers,' and seems particularly inappropriate in an executive order whose objective is greater openness."

While Preyer thought the proposed order an overall improvement over Nixon's 1972 edict, the ACLU and its allies found it "not appreciably different from its seriously flawed predecessor" and "even worse . . . in several respects."

For instance, the ACLU said, the Carter draft, unlike the directive implementing President Nixon's order, does not require the decision to classify national security information to be made upon origination of the document in question.

"For obvious reasons, 'post hoc' classification must be avoided," the ACLU said, "particularly since it can be used to bar the release of previously unclassified documents documents after they are requested under the Freedom of Information ACt."

In addition, the Carter draft apparently gives officials the power to exempt entire classes of information from an automatic six-year declassification rule and instead to continue their classification for 20 years. "Even the Nixon order requires document-by-document review for an extension longer than 10 years," the ACLU pointed out.

The Carter administration proposal sets forth 13 categories of information that can be classified, but they are broadly phrased, such as documents whose contents could br reasonably expected to "create or increase international tensions." The UCLU said the phrasing of the 13 categories was so inclusive "that it is hard to imagine any government information pertaining to national defense and foreign relations that could not fit within one" of them.

The Carter draft would strip 10 agencies, such as the Agriculture Department and the Federal Maritime Commission, of authority of classify information, but Preyer doubted this would have much of an impact.

Citing statistics compiled by his subcommittee, the North Carolina Democrat noted that the 10 agencies presently have only 22 employees with classification authorith - out of 13,976 such officials throughout the government in 1976. He added that the 10 agencies classified only 297 documents last year out of a total of 4.5 million that were stamped in the name of national security.

Others involved in the CLU study were Americans for Democratic Action, the Project on National Security and Civil Liberties, the Center for National Security Studies, the National Coaltion to End Repression, the Committee for Public Justice and the American Ethical Union. They urged fundamental changes in the Aministration raft.