MONROVIA, Liberia (AP) _ The government said today its forces still held the country's main international airport, but diplomats said rebels had overrun an American- managed rubber plantation on its outskirts.

The government acknowledged that airlines had halted flights to Robertsfield International Airport, 35 miles from Monrovia, the capital.

Fearful residents fled the city and some government soldiers abandoned key posts before the rebel advance.

Off the West African nation's coast, a U.S. Navy flotilla carrying 2,000 Marines stood ready to evacuate Americans and other foreigners.

President Samuel Doe remained at his presidential mansion in Monrovia, shielded by about 1,000 Israeli-trained troops.

Doe continued last-ditch efforts to end the 6-month-old civil war, meeting with church leaders who have offered to act as intermediaries.

The Liberian president begged the United States and other friendly countries ''to come to the aid of the Liberian people.''

''It is the wishes of the people of this country that America can do something to stop the bloodshed,'' he said Monday.

In Monrovia, people of the Mandingo and Krahn tribes loyal to Doe - himself a Krahn - packed their belongings to flee the city. They said they feared reprisals by rebels, who appeared to be closing in on the city of about 400,000 residents.

A U.S. State Department spokeswoman said 71 Americans, including 33 U.S. Embassy officials and their families, were evacuated Monday on a chartered flight.

The spokeswoman, Margaret Tutwiler, said in Washington that about 70 U.S. officials and 1,200 private American citizens remained in Liberia.

Today, diplomatic sources said rebels lobbed mortars and fired machine guns as they poured into the American-managed rubber plantation from across the Farmington River, the last natural barrier between the rebels and Monrovia.

The Bridgestone/Firestone Inc. rubber plantation adjoins Robertsfield airport, diplomats said. About 15 or 20 government soldiers remaining in the area returned rebel gunfire and then fled toward the capital, sources said.

Expatriates living in the area said there was a lot of shelling and shooting between the plantation's riverside marina and the Robertsfield Hotel, a three-minute walk from the airport.

Although rebels were believed in the hotel, they made no effort to capture the airport by midday today.

They also occupied the management offices of Harbel, the town owned by and operated by Bridgestone/Firestone, a subsidiary of the Japanese company Bridgestone Corp. Rebels surrounded the plantation's factory late Monday, stopping production, sources said.

Trevor Hoskins, Bridgestone/Firestone's executive director of public relations, said in Ohio that he talked Monday with the plantation's managing director, ''who indicated ... everything was quiet.''

Hoskins said the plantation, which produces 100 million pounds of rubber a year, covers 120,000 acres and includes 8,500 employees and about 90,000 residents, mostly dependents.

About 10,000 Liberians reportedly also moved onto plantation land seeking refuge from the fighting. Family members of the plantation's 30 foreign staffers were evacuated two to three weeks ago.

Rebels now control every major industrial concern in Liberia with the possible exception of Bong Iron Ore Mine, which has been cut off from the capital for days and is believed behind rebel lines.

Airlines suspended flights to Robertsfield on Monday, effectively closing the airport, after government troops fired on some of their own men, believing them to be rebels.

Diplomats and other sources who monitor military radio said that after the shooting incident the government soldiers deserted the checkpoint at Owensgrove, seven miles from the airport.

Lt. Gen. Henry Dubar, Doe's military commander, admitted to reporters that soldiers have been deserting their posts.

''The firing starts and they run away. They have to learn to stop panicking,'' he said.

Dubar said Monday that he hoped U.S. Marines would save Monrovia from the rebel incursion.

The U.S. State Department has accused rebel leader Charles Taylor of receiving support from the radical North African nation of Libya, but it also has said Marines will not intervene in support of Doe's government.

The rebels belong mostly to Liberia's Gio and Mano tribes and invaded this nation of 2.5 million people from neighboring Ivory Coast in December.

About 2,000 Gios and Manos overflowed the compound of St. Peter's Lutheran Church in Monrovia on Monday, where they were put under protection of the International Committee of the Red Cross.

The rebel National Patriotic Front of Liberia has demanded Doe's ouster, accusing his administration of corruption, economic mismanagement and human rights abuses.

Taylor was a close aide of Doe who headed the government agency responsible for disbursing public funds. He fled the country after Doe accused him of stealing $1 million from state coffers.

Liberia, founded in 1822 by descendants of freed U.S. slaves, in 1847 became the first independent country in black Africa.