Marines on Alert as Americans Flee Rwanda Fighting : Central Africa: About 300 U.S. troops muster in neighboring Burundi, while rebels claim to be within 10 miles of capital. Clinton deplores ‘tragic situation.’

Under cover of darkness, Americans fled escalating warfare in Rwanda by convoy late Saturday, a senior U.S. official said, while hundreds of U.S. Marines gathered in neighboring Burundi to help rescue foreigners from the ethnic bloodletting and civil war.

With a cease-fire between Rwanda’s rival Tutsi and Hutus quickly falling apart, President Clinton expressed concern about the “tragic situation” and about the safety of the approximately 250 U.S. citizens in the small Central African nation.

Rebels belonging to the Tutsi-aligned Rwandan Patriotic Front undertook an offensive north of Kigali, the capital city, the Reuters news agency reported. Fighting involving heavy artillery was said to be raging along a hilly region best known as one of the last homes of the rare mountain gorilla.

The rebels claimed to have advanced to within 10 miles of the capital.

Meanwhile, Americans and other foreigners were moving south “on anything with four wheels that moves,” a senior U.S. official said. Their destination was approximately 100 miles away in Bujumbura, the capital of neighboring Burundi, and the Associated Press reported that about 300 of the refugees--American and European--arrived there safely late Saturday and early today.

Two other convoys of Americans spent the night at a Danish mission station at the border between the two countries, U.S. military officials said.

The escape route through the southern part of Rwanda is relatively stable. U.S. officials said 170 Americans had left the capital and that 85 were still in Rwanda as of late Saturday.

Roughly 300 U.S. Marines were sent to Burundi on Saturday, “basically there to assist if anything starts to go wrong,” the senior U.S. official said.

The Marines were dispatched from U.S. warships in the Indian Ocean off Somalia.

In addition to the Marines, the Defense Department said that three huge CH-53 transport helicopters had been flown to Bujumbura along with four KC-130 tanker planes, which can be used as transports, and that four C-141 jet transports were sent to Mombasa, Kenya.

If needed, the troops could aid in mass evacuations--possibly today--of about 1,500 Belgian, 600 French and the remaining 85 U.S. citizens in Rwanda.

“The situation in Rwanda remains tense, and a sharp escalation of fighting has been reported in the capital city,” State Department spokesman Mike McCurry said Saturday. “The United States is taking steps to evacuate Americans from Rwanda, with the cooperation of local authorities.”

Rwanda, roughly the size of Maryland, is one of the poorest nations in Africa. It has been convulsed by violence since its president, Juvenal Habyarimana, and the president of Burundi, Cyprian Ntayamira, were killed late Wednesday when the airplane in which they were flying crashed as it approached the Kigali airport. The government said the plane was brought down by rocket fire from unidentified forces.

The two leaders, both Hutus, were returning from a regional summit in Tanzania intended to end years of violent spasms that have taken the lives of tens of thousands of the majority Hutus and minority Tutsi.

Belgium said it had sent elite paratroop units to Rwanda, its former colony, and French troops were said to have taken up positions in central Kigali.

There were conflicting reports about whether the contingent of about 300 French paratroopers had succeeded in securing the airport. Col. Luc Marchal, commander of Belgian forces serving with a U.N. peacekeeping unit, said Rwandan government forces opposed to the international effort later blocked the runway with firetrucks.

But in Paris, the Foreign Ministry said that French troops had evacuated 43 nationals by air and that other rescue flights are planned.

Dr. Pierre Harze, a spokesman in Paris for the humanitarian organization Doctors Without Borders, said the wounded and the dead in Rwanda’s capital “can be counted by the thousands.”

“There are a huge number of bodies in the street,” he told the Associated Press, relaying a report from staff members in Kigali.

Belgian television, which has two correspondents in Rwanda, carried several eyewitness reports Saturday that provided a picture of mounting confusion.

In one account from Kigali’s main hospital, medical coordinator Fabienne Dorlencourt described scenes of horror.

“I’ve seen about 150 bodies here, but the real figure (for the area around the hospital) is likely to be 300 to 400,” she said. “The wounded seem to have been injured mainly by machete and grenade attacks. It’s total anarchy.”

Prisoners were ordered to dig mass graves for the victims, Radio France Internationale reported.

Western diplomats were trying to reach all foreigners by radio to urge those willing to risk an overland journey to make their escape. U.S. personnel and their dependents--roughly half the Americans in Rwanda--were ordered to leave. Missionaries make up most of the rest of the U.S. population there.

A senior U.S official, speaking on condition of anonymity, said that once the evacuees reach Bujumbura they are to be flown to Kenya.

“It is mostly a civilian operation, with cooperation from local authorities and Rwandan security,” he said of the convoys. “There’s a lot of refugee traffic under way.”

Secretary of State Warren Christopher conferred by telephone throughout the morning with Gen. John M. Shalikashvili, chairman of the Joint Chiefs of Staff, and Anthony Lake, Clinton’s national security adviser. He also spoke early Saturday with the U.S. ambassador in Rwanda, David Rawson, to discuss options for “the ordered departure of U.S. personnel, their dependents and other American citizens,” McCurry said in a written statement.

“There are no reports of specific threats against Americans in Rwanda,” McCurry said, adding that as of midday in Washington, “things are proceeding smoothly.”

The State Department spokesman said the United States was participating in informal discussions in the U.N. Security Council on the violence in Rwanda, the safety of foreigners and the status of the U.N. mission there.

In his weekly radio address, Clinton said he is “deeply concerned about the continuing violence following the assassination of the president, the prime minister and other officials, as well as some of our United Nations peacekeepers” in Rwanda.

Similarly, he said, he is “very concerned” about the safety of the Americans there. “I want you to know that we’re doing all we can to ensure their safety,” he said.

In Kigali, the Speaker of the Parliament, Venat Sindikubwabo, announced the formation of an interim government. The Speaker, an ally of Habyarimana, the assassinated president, said on state radio that he is forming the government to restore order and that he wants to contact the rebel Rwandan Patriotic Front to set up a transitional government within six weeks, Reuters reported.

The overture to form the transitional government was rejected by the rebels.

“The RPF has irreversibly decided to fight this clique. . . . Let us work together to find and bring to book these murderers,” Paul Kagame, the rebels’ military leader, said in a statement said to have been broadcast repeatedly by a rebel radio station. Anyone standing in the way of the rebel front, he said, “will be considered an accomplice of the murderers and dealt with accordingly.”

Killed in the latest round of violence were Prime Minister Agathe Uwilingiyimana, a Tutsi, and other political leaders, human rights advocates, aid workers, nuns, priests, ordinary Rwandans and 10 Belgian soldiers, part of a 2,500-member U.N. peacekeeping unit. Rwanda was a colony of Belgium that gained its independence in July, 1962.

The rebels began their violent campaign, which has resulted in thousands of deaths, with an invasion from Uganda in 1990.

Isabelle Maelcamp, a researcher in The Times’ Brussels Bureau, contributed to this report.