President Reagan, rebutting Libyan leader Col. Muammar Qaddafi, said yesterday that the United States has evidence that Libya has sent assassins to murder senior U.S. officials.

"We have the evidence, and he knows it," Reagan told reporters who asked him about Qaddafi's denial of any plot to kill U.S. leaders and his demand that Reagan produce evidence to support several charges that hit teams have been dispatched to the United States on Qaddafi's orders.

Reagan did not make public any such evidence, but he convened a National Security Council meeting at which economic options to counter Libya were discussed amid indications that the United States is close to taking action.

When Reagan was asked during his brief meeting with reporters whether the United States can stand by idly, he replied: "Maybe you've just caught me before we've had a chance to counsel on this."

Except for his remark that Qaddafi, who called Reagan "silly" and "ignorant" for believing the assassination squad reports and "a liar" for spreading them, knows Washington has the evidence, Reagan jocularly turned aside other questions during a brief meeting with reporters in the White House press room.

Asked about Qaddafi's harsh words about him, Reagan replied: "I wouldn't believe a word he says if I were you."

Reagan, around whom security has been increased, was asked if he feels adequately protected and joked about the press room. "Yes," he said, "if I didn't think I was adequately protected, I wouldn't come into this room."

While the administration has not backed up its claims publicly with evidence, reports have been leaked to news organizations that a defector walked into a U.S. diplomatic mission in Western Europe within the last month and brought with him detailed descriptions of the 10 men, most of them Libyans, who reportedly make up the hit teams. The defector reportedly was also aware of their instructions and some details of their training.

One well-placed source said reports about what the Libyans are planning have included "lots of speculation" and amount to what might best be described as "a plausible scenario" based on "a limited amount of knowledge."

With that understood, this source said, authorities are trying to guard against tactics such as those used in the September ambush attack near Heidelberg against the commander of U.S. Army forces in Europe.

In that incident, which was linked to West German terrorists, two rocket-propelled grenades and a volley of bullets were fired, severely damaging the rear of Gen. Frederick J. Kroesen's armor-plated car. Kroesen was not seriously injured.

Members of the Senate Intelligence Committee, briefed by an unnamed Central Intelligence Agency official yesterday, supported Reagan's actions.

Sen. Henry M. Jackson (D-Wash.) said: "The statements made by the administration are correct. It's a serious problem." He dodged questions about whether any members of Congress reportedly are Libyan targets. Jackson also said administration officials had been justified in going public about the threats.

The president is scheduled to chair a second National Security Council meeting today. Having the president preside over the NSC on consecutive days is unusual and reflects the urgency with which the White House is considering the situation.

The problem confronting Reagan is that economic options are not guaranteed to work and for the most part require cooperation by other nations.

One option is a boycott of Libyan oil, but oil company executives say other customers would buy that oil unless the United States can win agreement from Britain, France, Italy and Japan to join a boycott. Chances of such international agreement are slight, administration sources said.

Only British cooperation would be necessary to close the oil fields temporarily by depriving Libya of technicians vital to operation of the fields. The technicians are American and British, and their companies could be ordered to withdraw them from Libya.

In the short term, the Libyans would be hurt. Eventually, they probably would have to turn to the Soviet Union for technicians, giving Moscow greater influence and control over Libya and its oil.

U.S. oil companies had not been told of any government decision yesterday, and industry officials said they had not been given fresh guidance. Last summer, the State Department advised U.S. citizens to leave Libya, but the government has yet to make any concerted effort to stop operations of the six U.S. oil companies doing business in Libya.

"We're trying to take our signals from the U.S. government," one oil industry source said. "But so far we're being told not to push any panic buttons."

About 1,500 U.S. citizens, mostly oil workers and their dependents, remain in Libya.

The State Department took a laconic view of the situation. According to spokesman Dean Fischer, the government is working on a comprehensive "review of our political and economic relationships with Libya," which began almost three months ago.

There was no indication about when the review would be finished, and Fischer said work on it has not been speeded up in connection with the reported assassination threats. "It is not the sort of subject that lends itself to quick acceleration," he said.

According to the State Department, direct imports of crude oil and refined products from Libya have dropped substantially, averaging 274,000 barrels a day in August compared to an average of 552,000 in 1980. Current imports are believed to be well below the August level.

Senate critics have pointed out that as of late summer the federal government was this country's fourth largest importer of Libyan oil. Of 32 importers on record, only three oil companies import more than the government.

Sen. Gary Hart (D-Colo.) said the government's Strategic Petroleum Reserve included about 23.2 million barrels of Libyan oil at the end of October, a little more than 10 percent of the reserve's total.