COMBAT IN PANAMA : Noriega Loyalists May Hold Some American Civilians : Hostages: Pentagon is investigating ‘about a dozen’ cases of missing U.S. citizens. Bush says captors may hope to use them to bargain for safe conduct out of Panama.

President Bush said Thursday that an undetermined number of Americans may be held hostage in Panama by deposed dictator Manuel A. Noriega’s loyalists, who hope to use them as “a ticket to get out of town.”

At a White House news conference, Bush predicted that if the ousted dictator is captured, remaining resistance to the U.S. invasion will collapse and most hostages will be released. But he conceded that some of Noriega’s supporters might attempt to trade hostages for safe conduct out of the country once his fate is sealed.

The Pentagon said it is investigating “about a dozen” cases of American civilians who are missing and may be held against their will. But Administration officials said there is no firm information about how many American or other foreigners are captives.

“We don’t have a count,” Bush said. “And if there are a lot of them, we don’t know about it. . . . It’s very hard to know what’s going on when there’s a firefight and a battle, because we heard all kinds of rumors.”

Eleven scientists and technicians working on a Smithsonian Institution project on San Blas island off Panama were released Thursday after having been seized by Panama Defense Forces troops Wednesday. However, Madeleine Jacobs, a Smithsonian spokesman in Washington, said that the five Americans, five Panamanians and a Venezuelan are far from safe.

“Our group of researchers is still in the jungle somewhere between Carti and El Llano,” Jacobs said. “They are very tired, very hungry. They have literally walked over the mountains to reach this place.”

She said that the Army plans to send a helicopter to pick them up but that it had not done so by late Thursday afternoon.

Jacobs said the 11 “were not rescued--they were released by the PDF.”

CBS News said that one of its television producers, Jon Meyersohn, was still missing Thursday night. He has not been heard from since he was abducted by Panamanian gunmen from the Marriott Hotel on Wednesday morning. Two other persons seized with him were later released.

“We have made contact, through every known channel, with officials at the State Department, Defense Department, and the White House,” CBS News President David Burke said Thursday in a memo to employees. “We also have been working non-stop with countless other government and private individuals both in the United States and Central America.”

Pentagon spokesman Pete Williams said the Defense Department is investigating “about a dozen” reports of missing Americans. But he cited by name only Meyersohn and the Smithsonian scientists.

Army Lt. Gen. Thomas W. Kelly, director of operations of the Pentagon’s Joint Staff, said the U.S. military has received reports of “20, 30, 40, or some number (of Americans) who are being held against their will or are in a place where they feel threatened.”

“We are trying to find out where all of them are,” Kelly said. “We have a lot of reports. Some of the reports will prove to be true; some will prove not to be true. The primary mission for the forces we’re moving into Panama City today is to find and protect the lives of Americans.”

Kelly said that troops of the 82nd Airborne drove Panamanian forces out of the Marriott Hotel on Wednesday night, freeing 29 American civilians and 35 other captives.

Staff writer Thomas B. Rosenstiel contributed to this story.