FRANKFURT, West Germany (AP) _ Americans have joined the investigation of two captured gunmen thought to be IRA members, officials said Friday, and a television report said one may be a major arms buyer for the Irish guerrillas.

West German police captured the heavily armed men late Tuesday after they crossed the border from the Netherlands near Waldfeucht, 45 miles northwest of Cologne. British military installations are located in the area.

The Supreme Court issued an arrest warrant Wednesday naming them as Gerard Thomas Hanratty, 29, and Terence Gerard McGeough, 30, and saying they were prime suspects in Irish Republican Army bomb attacks at British military installations in West Germany.

''We are currently working with investigators from Great Britain, the Netherlands, Belgium and the United States,'' Alexander Prechtel, chief spokesman for the federal prosecutor's office, told The Associated Press by telephone from Karlsruhe.

Asked whether the FBI was involved, Prechtel said: ''We are starting to make contact with the FBI. The men are being sought in the United States for illegal possession of weapons, as far as I know.''

U.S. authorities in West Germany said they were unable to confirm or deny the involvement of American investigators. ''People here who follow such matters don't know of any such connection at the present time,'' U.S. Embassy spokesman Bob Heath said.

Britain's Independent Television News said Thursday night McGeough may be a top arms buyer for the IRA and is suspected of organizing recent arms shipments from Libya. Moammar Gadhafi, the Libyan leader is said to have backed the IRA for several years.

Asked about the report, Prechtel said: ''We have no official information about the men's role in the IRA. We are currently working with British authorities to try to establish that. ''British authorities have told us that McGeough and Hanratty had been on the run for years.''

West German and international authorities are working together to trace the men's previous activities, he said.

Arresting officers found two AK-47 assault rifles and three .38 caliber pistols in the Irishmen's car, Prechtel said.

He quoted ballistics experts as saying one of the rifles probably was used in a July 13 bombing attack on a British army barracks in Duisburg and the shooting May 1 of Royal Air Force members in the Netherlands.

Nine soldiers were wounded at Duisburg. One was killed and two were wounded at Roermond in southern Holland.

McGeough and Hanratty are being held in a maximum security prison, Prechtel said.

The IRA, almost exclusively Roman Catholic, is fighting to drive Britain from Protestant-dominated Northern Ireland and unite it with the Irish Republic, which is 95 percent Catholic.