President Reagan, claiming that leaks of classified information have become "a problem of major proportions within the U.S. government," yesterday ordered a sharp crackdown on official contacts with the media, and warned that "all legal methods" will be used to investigate government employes who may have disclosed such information.

Directives signed yesterday by the president, based on recommendations by his new national security affairs adviser, William P. Clark, require that "all contacts with any element of the news media in which classified National Security Council matters or classified intelligence information are discussed" must have the advance approval of an unspecified "senior official."

Furthermore, officials interviewed then must provide a memorandum about what was discussed.

The number of officials with access to classified documents and internal deliberations also will "be kept to a minimum."

Acknowledging "the government's lack of success in identifying the sources of unauthorized disclosure" of classified information, the directive says this situation "must be remedied and appropriate disciplinary measures taken." From now on, the directive warns, government employes who have had access to information that leaks out "will be subject to investigation, to include the use of all legal methods."

Although the presidential statement is directed at disclosures about the White House's top-level National Security Council and other intelligence information, White House officials who briefed reporters last night said the new rules are meant to apply not only to officials on the NSC staff but also to those in the departments of state and defense and the intelligence community.

The White House officials, who could not be identified under rules of the briefing, say the new directives flow from a "virtual hemorrhage of leaks in the national security area which the president believes have hampered formulation of foreign and defense policy."

Asked for examples of such damaging leaks, the officials cited the recent reports of the administration's decision on the sale of fighter planes to Taiwan. The officials insisted that there has been a string of other damaging leaks, but declined to give further examples.

When reporters asked whether the administration would no longer leak classified information intentionally to support its case on certain issues and reminded the officials that concern over leaks had caused the Nixon administration to set up the ill-fated "plumbers" operation, one official said:

"Every president has been concerned about this problem. Every president has taken remedial steps to deal with it. This president is attempting to do it . . . to shut these leaks down."

In his statement, the president referred to the constitutional responsibility for protecting freedom of the press. "But it also requires that government functions be discharged efficiently and effectively," he said, and the disclosure of unauthorized information with impunity "must not be allowed to continue."

In an accompanying statement, Clark said, "We fully recognize the paradox inherent in our system." He said the measures should not be construed as criticism of the press. Rather, he said, "The press has been doing its job--collecting information--better than the government has been doing its job--protecting national security information."

The new directives appear to be one of the first actions by Clark, who heard the president complaining about the leaks of memorandum and policy considerations at a Cabinet meeting last week, his first since coming to the White House from the State Department.

The Reagan administration has had one of the most restrictive press information policies in the national security area, with reporters denied access to officials on the NSC staff and with the CIA, both of which were frequent sources of background information under previous administrations.

There were a number of unanswered questions at the briefing last evening. Officials said it was not yet clear who the "senior official" would be who would approve interviews, but they suggested it would probably involve one official in each agency rather than a single "czar." Asked if "all legal methods" of investigation included lie detector tests, officials said they weren't in a position to answer.

Asked if all requests for interviews would have to be approved, the officials said the restriction was limited to those dealing with classified subjects.

When it was pointed out that reporters are not cleared for classifed information and do not routinely ask to discuss it, the officials said, "Let's see how that works out."

Reporters were summoned on short notice to the White House to receive the Reagan and Clark statements and an announcement of the new NSC "structure," which officials said was basically "a re-statement of what now exists."

Supporting their view that leaks were hampering administration policy, the officials read another statement that claimed "some leaks have resulted in the compromise of sensitive intelligence sources and methods, in some cases endangering lives. Secondly, in several important cases, leaks to the press have preceded presidential discussions of highly sensitive foreign policy decisions," thereby reducing the president's options. No examples were provided.