MANAGUA, Nicaragua (AP) _ Eight West Germans released by U.S.-backed Contra rebels after nearly a month in captivity were en route to Managua today for medical checkups. One of them has hepatitis and urgently requires treatment, government sources said.

The rebel Nicaraguan Democratic Force, or FDN, released the Germans at 6:30 p.m. (8:30 p.m. EDT) Tuesday in the hamlet of Presillitas, near where they were captured May 17.

The four men and four women, volunteers building low-cost housing, were freed half an hour after a deadline set by the leftists Sandinista government. President Daniel Ortega had threatened military action if the deadline was not met.

The eight were en route to a military hospital in the capital, said a government official who spoke on the condition of anonymity.

One man, identified as Siegfried Ruettig, was suffering from hepatitis and was being transported by ambulance, the official said.

The other seven - Reingard Zimmer, Astrid Stelter, Juergen W. Kuhr, Dirk Diethelm Hegmanns, Angelika Goetz, Doris Altenburg and Dominik Dihel - traveled in two small buses, said another source who also spoke on condition of anonymity.

The buses were accompanied by Nicaraguan and West German government officials and Gonzalo Ramirez, president of the Nicaraguan Red Cross, the source said.

West German Foreign Minister Hans-Dietrich Genscher said in Bonn that Hans- Juergen Wischnewski, a leading lawmaker of the opposition Social Democratic Party, had taken charge of the hostages in Nicaragua.

The director of the military hospital scheduled a news conference for later today, the Defense Ministry said in a statement.

Genscher said he was grateful to everyone involved in getting the hostages released. He told reporters that ''the United States made its influence count'' in the negotiations. The U.S-backed FDN is the largest of several rebel groups known as Contras battling the Sandinistas.

Presidential spokesman Manuel Espinoza said on government Voice of Nicaragua radio that 15 Nicaraguan civilians were released along with the eight Germans. He did not identify the civilians.

The Germans were captured during a Contra attack on the village of Jacinto Baca, 160 miles southeast of Managua.

Before the hostages were released, Sandinista groups captured two FDN rebels who were scouting an escape route from Presillitas, the Defense Ministry said in a statement Tuesday.

The two rebels gave the military information that helped Sandinista troops apply ''constant pressure'' on the rebels holding the Germans, the statement said. It did not say what type of pressure was applied.

The Defense Ministry said military pressure and ''world condemnation'' of the capture forced the Contras to release the Germans.

But Frank Arana, an FDN spokesman in Tegucigalpa, Honduras, told The Associated Press there was no interference from the Sandinista military.

''Our patrols did not encounter any problems of any nature in entering or leaving,'' he said. ''The entire operation was a success and in an environment of tranquility.''

The Nicaraguan government said the Germans were released to the Sandinista military. Arana, however, said the Germans were released by a Contra patrol to representatives of the West German government at a church in Presillitas.

Arana said the release came about as a result of secret negotiations in Managua and Tegucigalpa between FDN leaders and West German officials.

Nicaragua initially set a deadline of 6 p.m. Monday, but Ortega extended that for 24 hours at the urging of West German Chancellor Helmut Kohl.

Last Saturday, the FDN claimed Sandinistas troops opened fire on one of their patrols holding the captives in southeastern Nicaragua, interfering with a planned release. The report was denied by the government, and neither version could be independently verified.