The administration is planning some form of economic sanctions against Libya but is still in the middle of high-level discussions to determine their scope, according to senior administration officials.

President Reagan convened a session of the National Security Council again yesterday to take up the issue for the second consecutive day, and the group adjourned in mid-afternoon without reaching a conclusion.

One of the ideas reportedly under consideration involves asking U.S. allies from the ranks of the major industrial oil-importing countries to join in an effort to cut the market for Libyan oil. But to do this, officials say, the United States would have to take the lead.

"This president feels that it's inconsistent to pay a big bill to Libya every year while at the same time asking our friends to stop dealing with them," one knowledgeable source said.

The White House yesterday afternoon was said to be within 24 to 48 hours of briefing congressional leaders on what it intends to do. Two press statements, apparently differing in the sternness of their rhetoric, reportedly have been prepared.

Reagan himself said Monday that "we have the evidence" that Libya's leader, Col. Muammar Qaddafi, had sent assassination teams to murder top-ranking U.S. officials but, rather than follow up with details, White House officials yesterday deplored leaks to the media about the alleged teams.

White House communications director David Gergen said, "The White House has made it very clear to the various departments that the president condemns these leaks."

Late yesterday, Sen. Gary Hart (D-Colo.) proposed a sense-of-the-Senate resolution declaring that Congress "would support and act favorably on a decision by President Reagan to impose a prohibition on the import of oil from Libya," but Senate Majority Leader Howard H. Baker Jr. (R-Tenn.) persuaded him to withdraw it.

Baker said he had just spoken with White House chief of staff James A. Baker III who told him the president needed more time to decide what to do. The Senate leader urged that Reagan be given "maximum flexibility" until then.

"This is a delicate moment," Sen. Baker said.

Hart described his resolution as "an effort to halt as soon as possible the American financing of international terrorism, especially when that terrorism is directed against our country."

"We are paying for Libyan terrorism, period," Hart declared. "Whether or not there is a hit team in this country, we are paying for terrorism."

The State Department estimates that U.S. purchases from Libya will total about $6 billion to $7 billion for 1981 and that U.S. sales to Libya will total more than $700 million. Machinery and transport equipment are the leading U.S. exports to Libya.

Reports from Libya have asserted that the United States is seeking support in Europe. The Libyan news agency, JANA, said over the weekend that the CIA had "sent to NATO a secret report which instigates West European countries to counter Libya's policy and foil economic relations with this state."

The JANA report attracted special attention from the Soviet news agency, Tass, which distributed a news item about it.

There was increasing clamor yesterday for disclosure of at least some of the evidence of the alleged assassination scheme, said to revolve around two five-member hit teams that may have entered the United States.

Sen. Christopher J. Dodd (D-Conn.) said: "This thing is so hyped up it is taking on a life of its own." Dodd is a member of the Senate Foreign Relations Committee, which received a secret briefing on the reported Libyan plot from FBI officials Monday afternoon.

At the White House, Gergen was pressed at the daily news briefing to make public some of the evidence the administration says it has. He said details may be produced at some future date.

Other White House officials said they are rankled by media suspicion that the hit teams are some sort of smokescreen created by the administration. "There is a misconception that we wanted this information out," one said. "Nothing could be further from the truth."

These officials also said an effort is being made to determine the origin of the leaks, with the intent of punishing those involved.

A former Carter administration official said there were several instances when Carter was in office of reported threats against the president that seemed credible enough to step up security quietly, but word of those episodes did not become public.

Gergen took strong exception to suggestions that the administration is promoting the hit team reports to lay the groundwork for action against Qaddafi.

"I personally find it astonishing that people think we somehow would go through this exercise unless we took it seriously," he said. "We are not engaged in some public relations ploy here . . . . We regard this, and the government regards this, as serious."

Gergen also said it would be wrong to think that Libya was "the sole focus" of the unusual, back-to-back NSC meetings this week. But he acknowledged that it was a topic, saying, "clearly it's being discussed by the president with his top advisers."

Officials of several of the U.S. oil companies still operating in Libya said they are waiting for the government to inform them of its plans. About 1,500 U.S. citizens, mostly oil workers and their dependents, remain in Libya, according to the State Department.

The Senate Foreign Relations Committee had scheduled a hearing this morning on possible economic options regarding Libya, but it was postponed yesterday until February.

State Department officials reportedly informed the committee that they were not prepared to testify. Senate staff aides said the session had been scheduled a couple of weeks ago before the atmosphere began to heat up.

The New York Daily News reported yesterday that the infamous international terrorist known as "Carlos" is suspected to be masterminding the assassination scheme.

NBC News reported, on the other hand, that information provided to the Senate Intelligence Committee in another Monday briefing was inconclusive, that "Qaddafi was overheard boasting that he would have Reagan assassinated" but that there was "nothing more conclusive from the informant."

The report by correspondent Tom Pettit also quoted Sen. Patrick J. Leahy (D-Vt.) as having said after the briefing: "There is no hard evidence at all."