U.S. Marines evacuated 61 Americans and 12 others from war-torn Liberia yesterday in an air-sea operation launched after a rebel leader in Liberia's civil war threatened to arrest all foreigners there.

The Pentagon said 255 Marines, using transport helicopters flying under protective cover from attack helicopters and jets, airlifted the evacuees from the U.S. Embassy in Monrovia, the Liberian capital, and from two nearby communications sites.

The Pentagon said the Marines encountered no resistance and no shots were fired during the eight-hour operation. Military officials said no Marines or evacuees were injured.

White House press secretary Marlin Fitzwater said the Marines, part of a four-ship expeditionary force trained in special operations, would "remain as long as necessary to assure the security" of U.S. citizens there, including a "skeleton staff" of 46 at the embassy, along with U.S. Ambassador-designate Peter de Vos. As many as 500 U.S. citizens, many of them with dual citizenship, remained voluntarily in the country.

Although the four U.S. ships have been stationed off Liberia for the past two months, Fitzwater said that the rescue operation "does not indicate or constitute any intention on the part of the U.S. government to intervene militarily in the Liberian conflict." The United States has repeatedly stated its neutrality in the months-long war in which two competing rebel forces have been battling to oust President Samuel K. Doe, who took power in a 1980 coup.

President Bush ordered the rescue operation late Saturday after Prince Johnson, one of the rebel leaders, threatened foreigners in Liberia, Fitzwater said. He said the decision was made at Camp David, where Bush met Saturday with key advisers on the crisis in the Persian Gulf following Iraq's invasion of Kuwait.

While denying any relationship between "these two actions in separate parts of the world," Fitzwater said the Liberian operation "does, of course, point out that President Bush is extremely concerned about the welfare of American citizens." Iraq, he said, was surely aware that Bush has "acted time and time again" to protect U.S. citizens.

Congressional leaders were notified of the Liberian action shortly after 5 a.m., the White House said. Sen. Paul Simon (D-Ill.), chairman of the Senate Foreign Relations subcommittee on African affairs, said, "The president's action is a proper one and I support his decision." Other congressional response indicated no objection.

The rescue effort, called Operation Sharp Edge, was the first evacuation mission by Marines since one they ran in the early 1980s from Beirut. Marine expeditionary units have been alerted to prepare for potential rescues several times in recent years, including during coup attempts in the Philippines and unrest last year in Burma, now called Myanmar.

There was no reported response to the evacuation from Johnson, whose troops reportedly are trying to storm Doe's fortified mansion in the capital. In a radio broadcast, Charles Taylor, the other rebel leader -- whose forces are confronting government troops east of the capital -- reportedly called on the Liberian population to "defend your country" and "oppose all foreign intervention."

But Randolph Cooper, a Washington spokesman for the Taylor-led National Patriotic Front of Liberia, told Reuter that the group was cooperating in the evacuation. "We're not against foreigners, and we'll do anything to ensure their safety," Cooper said.

The rescue operation began a few hours after dawn yesterday, Liberian time, when 17 aircraft were launched off the helicopter carrier USS Saipan. As two AV-8B Harrier attack jets armed with Sidewinder and surface-to-ground missiles flew a protective air cover, two giant Marine Corps CH-53 Sea Stallion helicopters carrying members of a reinforced rifle company trained in special operations headed across the water for the U.S. Embassy in Monrovia.

Meanwhile, five CH-46 Sea Knight helicopters with two AH-1 Sea Cobra attack choppers flying cover headed for one of the two communications sites, in the community of Brewerville, 12 miles northwest of Monrovia.

Another group of four Sea Knights with their own Cobra escorts flew to the other site, east of the city on the road to Roberts International Airport.

The installations are Central Intelligence Agency and Defense Department collection-and-relay facilities for diplomatic and intelligence communications throughout Africa. A senior official said "normal procedures" for protecting classified materials were followed at the facilities, and that sensitive material was either destroyed or taken along by a total of 21 departing U.S. officials and workers.

Americans were evacuated six weeks ago from a third communications site, the Voice of America transmitter located close to the giant Firestone Co. rubber plantation north of Monrovia. Since then, Liberian personnel have operated the facility.

The transport helicopters deposited the communications workers on the Saipan, then flew to the embassy to pick up other evacuees. Two of the workers taken from one of the communications stations hopped helicopters to the embassy to remain in Liberia, officials said.

After two evacuation shuttles from the embassy, a total of 61 Americans had been landed aboard the Saipan, along with two Italians, a Canadian, a Frenchman and eight Liberian dependents. Most of the 255 members of the Marine rifle company were left at the embassy to bolster its small security force, officials said. The evacuees were scheduled to be airlifted from the Saipan to Freetown, Sierra Leone, northwest of Liberia.

Late yesterday, a helicopter ferrying a group of evacuees from the Saipan to Sierra Leone was forced to put down in that country after experiencing technical difficulties, U.S. officials said. No one was reported injured, and a second helicopter flying close by landed and picked up the stranded passengers.

Virtually all U.S. citizens remaining in Liberia were warned of the danger of remaining there and invited to depart, but many declined, administration officials said. Those remaining voluntarily include a few businessmen and agricultural advisers, missionaries, spouses of Liberians and U.S.-born children who are living with relatives while their Liberian parents work in the United States.

The United States also had agreed to evacuate citizens from a long list of other countries, including the Soviet Union and Israel, but officials said yesterday that most already had withdrawn their diplomats and personnel.

Most of the estimated 5,000 Americans who were in Liberia two months ago have departed, including hundreds who left on charter flights in July, after the international airport had shut down.

Describing conditions in Liberia during his White House briefing yesterday morning, Fitzwater portrayed a country nearly shut down in the midst of civil war, and a population under siege. He said sporadic shooting occurred Saturday near the embassy and throughout the downtown area. All major stores were closed, he said, and there was no publicly available water, electricity or phone service. Food shortages, he said, have intensified, and fuel is unavailable in most parts of the country.

The United States backed Doe both diplomatically and financially for much of his rule, but has avoided taking sides since the rebel groups launched an effort seven months ago to topple him. The rebels accuse Doe of corruption and human rights abuses.

The United States has long had what it calls "a special relationship" with Liberia, in which are located more U.S. military and intelligence arrangements than in any other sub-Saharan African country. CIA rebroadcasting antennas and signal-boosting amplifiers are part of its communications complex, and an Omega navigation system transmitter -- one of eight worldwide -- serves as a backup system for underwater guidance for U.S. missile-launching submarines.

In addition, a mutual defense treaty allows basing and staging of the U.S. Rapid Deployment Force from Liberia, officials said, and the country has granted the United States short-notice landing rights.

Another Marine amphibious group is scheduled to leave the East Coast early this week for possible deployment to the Persian Gulf area. Originally, these four or five ships were supposed to relieve the group off the coast of Liberia. But because of the Iraqi invasion of Kuwait, military officials plan to keep units in both regions.

The Marines have no other amphibious groups that could be used for an evacuation in the Middle East, officials said. The aircraft carrier USS Independence has reached the area of the North Arabian Sea and could be used for some evacuation efforts with helicopters and small aircraft.

The Saipan, which will remain off the Liberian coast with the three other ships, is equipped with operating facilities for helicopters and the Harrier, a jet that can land and take off like a helicopter and fly like a fighter. In addition, the ship contains a large garage for trucks and armored vehicles, and has extensive medical facilities, including an operating room.

About 2,200 Marines are assigned to the four-ship group. In addition to the Saipan, the group includes the USS Sumter, a tank-landing ship; the USS Ponce, an amphibious transport dock; and the fast frigate USS Patterson.

Staff writer Dan Morgan contributed to this report.