The CIA has concluded that an assassination attempt was directed against Libyan leader Col. Muammar Qaddafi two months ago and that, although Qaddafi was not seriously injured, he probably was nicked by a bullet in the jaw, according to informed officials.

Foreign news reports of the assassination attempt initially were dismissed last month, and the U.S. media gave them little or no attention. But a senior government official said this week that the CIA now has sufficient evidence to confirm the reports.

The official said the plot was carried out by some members of Qaddafi's army, probably by one or more officers who had just returned from the Libyan invasion of Chad, and received no external support from any foreign country, including the United States.

The attempt on Qaddafi's life was placed during the last two weeks of December, shortly after the first major reports surfaced in the United States about "hit squads" allegedly sent by Libya to assassinate President Reagan and other high-ranking U.S. officials.

On Dec. 6 Qaddafi denied in an ABC television interview that any such squads or individuals had been sent. "We are sure we haven't sent any people to kill Reagan or any other people in the world," he said.

A well-placed source has said that one U.S. intelligence agency has had information for several months that the Israeli intelligence service would like to have Qaddafi assassinated.

Asked this week if the Israelis would assassinate the Libyan leader, a senior U.S. official said the Israelis would do so "if they thought it would earn them points in this country." This official said he is certain the Israelis were not involved in the December assassination attempt.

That attempt occurred while Qaddafi was visiting a headquarters area in the Libyan countryside, the officials said. One State Department report in early January said that Qaddafi had gone to Moscow for treatment and returned in early January.

Other sources said U.S. intelligence agencies had insufficient hard information to support this conclusion, and these sources said they doubted that Qaddafi went to Moscow during that period.

Initial news reports out of Rome and Tunis said that the assassination attempt occurred Dec. 19 and that an eastern area army commander, Col. Khalifa Khadir, was shot and killed by Qaddafi's security guards during the attempt. Qaddafi's driver reportedly was killed in the shooting.

At the time of the first reports of the attempt, Libyan embassies in various places, including Athens, denied the reports.

An unconfirmed report currrently circulating among those with good Libyan contacts in this country is that Qaddafi has lost confidence in his security forces and has replaced them with outsiders, in some cases Syrians.

Whatever may have happened in December, Qaddafi resurfaced publicly Jan. 5 to address the final session of the General People's Congress in Tripoli.

In a rambling speech carried live on Libyan radio he made indirect reference to the assassination reports.

He said, "Two weeks ago, I went to a region inside the country. I particularly inspected a strategic road now being built, linking southern and central Libya . . . . During these two weeks there were many rumors. I heard about them and we laughed about them a lot.

"I was in that region, and it was reported that I was in Moscow. Well, Moscow. First, I cannot go there this winter because of its sub-zero temperatures . . . .

"Such rumors circulate when one doesn't speak on the radio. I deliberately avoided speaking on the radio. And all of us, those who lead the revolution, deliberately avoid speaking on the radio or in the papers. Let the popular masses speak on the radio."

During the speech Qaddafi said that of the 4,000 Libyan students in the United States "30 of these students were recruited by U.S. intelligence and now they receive salaries from and work for the United States."

There have also been reports that as few as four and as many as 640 Libyans allegedly involved in the assassination attempt have been executed.

U.S. officials say they believe that some people have been executed, not an uncommon occurrence as the Qaddafi government goes through seemingly continuous leadership changes and purges.

On Jan. 9 Sudan's official news agency, SUNA, reported that Qaddafi had to put down a coup attempt in the eastern Libyan city of Benghazi earlier in the month.

In the last several years Qaddafi has overseen unsuccessful foreign adventures in Uganda and Chad, from which Libyan troops were withdrawn recently. Their failure has made his position with respect to the army significantly less secure, according to one U.S. government analyst.

These sources also say that groups and individuals who do not like Qaddafi are emerging into an organized opposition, adding another complication to his hold on power.