MONROVIA, LIBERIA, JULY 21 -- The following, transmitted by the Associated Press, is based on a pool report filed by foreign correspondents in Liberia.

Advancing rebel troops fought pitched battles with government soldiers near Monrovia's center today, and besieged President Samuel Doe expelled the U.S. military attache.

A Liberian government communique accused the head of the U.S. military mission, Col. David Staley, of supporting the rebels and urging government forces to defect.

In Washington, State Department spokesman Adam Shub confirmed that Staley left Monrovia after having been ordered out. Shub said the charges were "entirely without foundation."

"Our embassy has protested vigorously to the government of Liberia," Shub said. But, "in accordance with the normal diplomatic practice, we withdrew Col. Staley."

Heavy fighting drew closer to the center of the capital as government troops fought with the rebels in the port, a mile west of Doe's executive mansion. The rebels, who began their war to overthrow Doe in December, overran most of northern Monrovia on Friday, capturing the port. Reporters saw government tanks and troops taking up defensive positions today on their side of the two bridges connecting the center of the city to the port.

The rebels advanced to within six miles of the mansion of Doe, who has refused their demand that he leave the country.

Doe was entrenched with about 500 soldiers of his Krahn tribe. Many Krahn fear a massacre at the hands of the Gio and Mano tribesmen who make up the bulk of the rebel force of Charles Taylor, a former official of Doe's government.

Journalists on both sides of the war have reported seeing soldiers killing fighters and civilians of tribes aligned with the other side. Fifteen government soldiers were reported summarily executed by the rebels Friday, an unconfirmed report said.

Doe, in a news release sent to the British Broadcasting Corp. in London, alleged the expelled U.S. military attache had used U.S. government vehicles to provide supplies to the rebels and had given them advice. The statement also said Staley used abusive language to describe Doe in front of Liberian officers.