The U.S. State Department's top African affairs expert came here today on his second unannounced trip to Liberia in three weeks following reports that the country's new military rulers may be moving closer to Libya.

Richard Moose, assistant secretary of state for African affairs, arrived this afternoon following apparently incorrect reports that Master Sgt. Samuel Doe, the military head of state, was leaving for Tripoli today. Four top Liberian officials went to Libya today, but Doe apparently was not among them.

Moose's trip here is a reflection of growing U.S. concern that Liberia, for many years America's closest African ally, may move into a more radical orbit in search of assistance for its strapped economy and adopt a more nonaligned posture.

At a brief press conference when he arrived today, Moose declined to specify his reasons for the two trips in three weeks -- four since the April coup that brought Doe to power -- except to say that it involved "new" money for Liberia.

Asked if it was in response to reports that Doe would be going to Libya today, Moose responded, "I won't say there is no connection."

The Libyan leader, Muammar Qaddafi, whose government is growing increasingly isolated on the African continent, recently sent a delegation here, reliable sources report, offering crude oil or a large infusion of monetary aid.

The U.S. government, in addition to the desire to protect its traditionally close relations with Liberia from Qaddafi's influence, also has some important electronic military installations here as well as the Voice of America's African relay station.

Four government officials left for Libya this morning. They included the foreign minister, Gabriel B. Matthews, and the minister for planning and economic affairs, Togba Nah Tipoteh. Both civilians have reputations for exerting strong influence on Liberia's 7-month-old military government.

U.S. officials recently charged that Qaddafi has sent several thousand troops into Chad to aid one side in the civil war raging there. In recent months, Senegal, Gambia and Ghana abruptly have broken diplomatic ties with Libya.

Liberia has been ruled since the April 12 Army coup by a military government. Sgt. Doe, 29, heads an all-military, 28-member People's Redemption Council, which functions as the executive body of government over a mixed military and civilian Cabinet.

Since taking power, the new government has faced several severe financial crises that it inherited from the assassinated president, William Tolbert. Shortly after coming to power, the new rulers discovered that the government, which in good years receives revenues of $250 million, was $700 million in debt and faced declining revenues from its major export, iron ore. The government averted a major oil payments crisis Friday with the help of three New York banks: Chase, Citibank and Bankers Trust.

In addition, there has been capital flight of some $35 million since April as Lebanese merchants, who dominate retail trade here, and the former ruling political group of Americo-Liberians -- as the descendants of freed American slaves are called -- transferred savings and deposits out of the country. Two weeks ago, Doe gave a tough speech announcing a tight austerity budget and forced savings program. Besides slashing expenditures under an International Monetary Fund stabilization program, Doe announced a hiring freeze in all government services.

Moose characterized Doe's decisions as "tough and courageous," adding that it was in part that speech that provided the atmosphere in which more American aid could be offered.

Moose also revealed that Chase Manhattan, Citibank and Bankers Trust provided almost half of an $11 million oil payment by the deadline Friday. The Liberian government had come up with half of a slightly overdue payment. Informed sources said Liberia could have lost its international credit rating if the payment had not been made by Friday.