The State Department ordered all nonessential U.S. government personnel and their dependents to leave Liberia last night and strongly advised the approximately 1,100 private U.S. citizens there to leave immediately "due to deteriorating conditions," according to spokeswoman Sondra McCarty.

As a Liberian rebel army pressed to within 25 miles of the capital of Monrovia, the Defense Department dispatched a six-ship Marine amphibious group to the Liberian coast to stand by to evacuate U.S. citizens, Pentagon spokesman Pete Williams said. It was not expected to arrive until Monday.

Williams said the USS Saipan, a helicopter assault carrier, and five support ships comprising the Mediterranean Amphibious Ready Group, which carries a detachment of 2,100 Marines, was ordered "as a precaution to take up a position in international waters {off Liberia} in the event they are needed to help American citizens -- and other noncombatants -- who need to leave and cannot do so by commercial means."

Another Pentagon official said the Joint Chiefs of Staff on Wednesday issued a "warning order" to the amphibious group to be prepared to conduct a "noncombatant evacuation" of U.S. personnel and dependents off the Liberian coast. The flotilla left port at Camp de Canjuers in southern France Wednesday, an official said.

The United States maintains regional centers in Liberia for its diplomatic and intelligence networks, plus a large Voice of America complex. A large U.S. business community, including banks and rubber companies, long have maintained investments there worth as much $500 million.

Williams said U.S. officials have informed the government of President Samuel Doe that the ships had been sent.

The Associated Press added from Monrovia:

The rebels were reported yesterday to be ambushing troops within a few miles of the country's only international airport, at Robertsfield, about 20 miles from the capital.

Charles Taylor, leader of the rebel army, rejected any political settlement and vowed to seize Monrovia, while President Doe said he will not resign, heightening fears that the two armies will clash in the capital.

The United Nations canceled an emergency food program for refugees of the civil war yesterday, and its remaining foreign workers in Monrovia prepared to leave. It took the actions after a U.N. compound was attacked by government soldiers Wednesday and a guard was killed.

Doe made his comments during a meeting with diplomats to discuss the attack on the U.N. compound. One diplomat quoted Doe as saying: "I will not resign but will be the last person to leave" Monrovia.

That position represented a reversal for Doe, who reportedly told supporters at a rally last week that he would resign if that would help end the fighting.

On Wednesday, the National Assembly unanimously rejected a request from Doe to hold early elections and install an interim government. The lawmakers called on Doe to fulfill his promise to step down, a source said.

The rebel forces led by Taylor, a former civil servant whom the Doe government accused of embezzlement, invaded eastern Liberia five months ago from neighboring Ivory Coast. The fighting has killed more than 1,000 people in this nation of 2 million, founded in the 19th century by freed American slaves.

Taylor, who said he called the BBC from the port of Buchanan, affirmed his fighters would not stop until they had taken Monrovia and formed their own government. Taylor's rebels captured the country's main port of Buchanan, 95 miles east of the capital, five days ago.

The Standard newspaper in Monrovia reported that rebels had sent a telex to the manager of the Robertsfield International Airport, saying all employees should evacuate because an attack would occur soon.

Ghana Airways, the main commercial air link to Liberia, said on Wednesday it would no longer be flying into the country. However, several other carriers were still serving the airport.

Bridges to Guinea were reported to have collapsed under heavy traffic of refugees, but roads were open to Sierra Leone. Thousands of refugees have fled to neighboring countries.