The Justice Department will probe charges that U.S. authorities protected top Nazi Gestapo figure Klaus Barbie after World War II and helped him escape to Bolivia in 1951, Attorney General William French Smith announced last night.

The investigation will also focus on evidence obtained by the department that Barbie was in the United States on several occasions in 1969 and 1970, according to department sources. It will look at how Barbie got in and out of the country and at another report that he may have been dealing in arms.

"We view those allegations with deep concern, and a preliminary review of pertinent government files indicates these allegations have sufficient merit to warrant a comprehensive investigation," the Justice Department said in a statement.

Department sources said Smith changed his mind about the probe under mounting pressure from Congress, the White House and other outside groups interested in the issue. He had initially opposed it on the grounds that it was unlikely to lead to a prosecution, according to sources.

Allegations of U.S. involvement arose last month after Barbie was extradited from Bolivia to France for trial on "crimes against humanity."

Correspondence between the French Ministry of Justice and French army officers in Germany indicates that U.S. authorities blocked at least three French requests for the return of Barbie, known as the "Butcher of Lyons," to face accusations that he had sent thousands of Jews and French resistance fighters to their deaths.

Tom DeCair, a spokesman for Justice, said last night that the department has already started a preliminary review of allegations that "Barbie had a relationship with the U.S. government in the years after World War II and that the U.S. government assisted his travel to Bolivia in 1951. We view those allegations with deep concern . . . . Therefore, the Department of Justice is undertaking a full investigation. The object of the investigation is to develop a factual record of any relationship that may have existed between Klaus Barbie and the U.S. government at any time."

Department sources said that Allan A. Ryan Jr., head of the Justice Department Office of Special Investigations, will be detailed to conduct the investigation. Ryan's unit has been heavily involved in tracking down and prosecuting former Nazis living in the United States.

Barbie, 69, had been sentenced to death in absentia by a French military court, but time had expired for carrying out the sentence. He has been accused of responsibility for the deaths of 4,000 people and the deportation of 7,500 others to Nazi concentration camps.

The Senate Intelligence Committee has already begun looking into alleged links between Barbie and U.S. intelligence agencies.