President Reagan, asked to comment yesterday on a threat by Libyan leader Muammar Qaddafi to attack "Americans in their own streets" if the United States retaliates for last week's European airport killings, denounced "fellows who think it's all right to shoot 11-year-old girls."

Reagan's comment, in Los Angeles at the end of his New Year's holiday, came as his military advisers sifted through a Defense Department contingency list of bombing targets in Libya ranging from a government facility to antiaircraft sites, which could be reached by Navy and Air Force carrier planes and fighter bombers based in Britain.

However, there was no indication that the plans, by now a familiar exercise for U.S. military planners in the wake of terrorist incidents abroad, have been approved by senior Cabinet officers or Reagan. A Pentagon official termed the activity "prudent planning in case the president should ask us to do something" in retaliation for alleged Libyan support of the Dec. 27 terrorist attacks at airports in Rome and Vienna.

Fearing an attack, Libya sent its ships to sea yesterday and dispersed its aircraft around the country, U.S. officials disclosed last night.

[Israeli officials, also facing the issue of whether and how to retaliate for the terrorist attacks, came under further pressure yesterday after five surface-to-air rockets fired from Lebanon landed in northern Israel. Israeli officials threatened retaliation but took no action, citing difficulty in fixing responsibility.]

The contingency list, assembled during intensive sessions at the Pentagon and other military complexes in the last several days, is intended to pinpoint Libyan targets against which the president could retaliate without killing innocent civilians, according to informed sources.

The Joint Chiefs of Staff, it was learned last night, have recommended against attacking targets not directly linked to terrorists from Palestinian Abu Nidal's group, which the State Department has said is the prime suspect for the airport attacks.

The military contingency planning has looked at the use of FA18 bombers on the carrier USS Coral Sea, scheduled to leave Naples early today; F111 fighter bombers in Britain and B52 bombers based in the United States, officials said.

The B52s were considered an option earlier in the week, in part because Libya would not have known they were coming, whereas the United States would have tipped its hand if it had ordered the Coral Sea to cut short its port call, officials said. But now that the Coral Sea is leaving Naples on schedule, its bombers and the F111s in Britain have emerged as the favored military option if Reagan should order a military strike.

As in previous terrorism cases, planners at the Central Intelligence Agency, Pentagon, National Security Council and various military headquarters have been handicapped by scanty intelligence on the whereabouts of the renegade group headed by Abu Nidal.

Abu Nidal has been described by U.S. officials as the prime suspect in organizing the airport attacks, which killed five Americans in Rome, including 11-year-old Natasha Simpson, to whom Reagan referred yesterday. The president's comment came after Qaddafi praised the airport killings and threatened to attack Americans at home if the United States bombed his country.

In a report issued Tuesday, the State Department said that "since early 1984, Libya began to provide increased support" to the Palestinian group, "and Abu Nidal himself and many of the group's operations may have moved there within the last 12 months."

Department spokesman Charles E. Redman said yesterday that "around 1,500" Americans are believed to be in Libya. Although that estimate is about one-quarter of the number there before U.S. citizens were advised to leave in December 1981, it complicates any U.S. military planning, officials said.

"Given the erratic and irresponsible behavior on any number of occasions [by the Libyan regime] which has been amply documented, you are taking a risk by remaining in that country," Redman said, repeating a warning issued several times in recent years.

The Americans in Libya include employes of Libyan and third-country firms, their dependents and wives, and other relatives of Libyan nationals.

In addition, State Department officials said, four American oil companies continue to operate in Libya and employ U.S. citizens at times to help on specific technical problems.

"We strongly oppose travel to Libya by American citizens because of the danger to their own welfare imposed by the unpredictability of actions by the Qaddafi regime," Redman said yesterday.

Since Dec. 10, 1981, it has been a violation of U.S. law to travel to Libya on a U.S. passport without State Department validation. Journalists, humanitarian cases, American Red Cross personnel and people whose travels are deemed "in the national interest" receive such validations.

Redman said that U.S. economic measures taken against Libya since 1981 have been somewhat effective, but that the administration is now "looking at other things we could do." Additional measures, he said pointedly, would be more effective "if they were undertaken more widely by the international community."

U.S. exports to Libya fell from $860 million in 1979 to $200 million in 1984, he said. Current exports are primarily pharmaceuticals, farm products and nonstrategic manufactured goods. Libyan oil sales to this country dropped from $5 billion in 1981 to $9 million in 1984, according to Redman.

The administration's emphasis yesterday on economic retaliation against Libya contrasts with the harsher rhetoric of U.S. officials earlier in the week when spokesmen refused to rule out an American military response to the airport attacks and said they would welcome Israeli action. An Israeli source said many Israeli officials find it vexing to have the U.S. government ask Israel to do "the dirty work" on military retaliation, as if Tel Aviv needed Washington's permission to take such action.

While some U.S. officials studying targets in Libya find antiaircraft sites appealing because they carry little risk of inflicting what the planners call "collateral damage" -- the killing of civilians -- others warn that the Soviet Union has 1,500 citizens in Libya, including 600 at the antiaircraft sites.

Also, there is a risk of losing warplanes against antiaircraft sites, as a Dec. 4, 1983, retaliatory bombing raid in Lebanon demonstrated. Two Navy bombers were shot down by Soviet-supplied SA7 heat-seeking missiles, which have a range of slightly less than two miles. The Soviet Union recently sent Libya SA5 missiles with a range of 150 miles and probably has technicians at the sites, officials said.

There are facilities in Libya linked to terrorist activity, government officials said, but military actions against them are complicated by civilians in the target area and uncertainty about terrorist leaders' presence at the facilities. The same problems were among the reasons the United States never carried out its elaborate plan to bomb Baalbek, Lebanon, to retaliate for the terrorist bombing of the U.S. Marines' barracks at the Beirut International Airport in 1983.Staff writers Don Oberdorfer, John M. Goshko and Fred Hiatt contributed to this report.