The U.S. military is moving quickly to interrogate more than 2,000 Iraqi POWs -- including two generals -- for information about the location of chemical and biological weapons.

No tips have led U.S. forces to uncover any of Saddam Hussein's deadliest weapons.

However, U.S. officials said late Sunday troops have found a suspected chemical factory near the city of Najaf south of Baghdad that was being examined to determine whether it was involved in making weapons.

U.S. Central Command said in a statement that troops were examining "sites of interest," but did not elaborate. The statement said reports describing the location as a chemical weapons factory were "premature."

And none of Iraq's top Republican Guard units, whose leaders might know more, are yet under U.S. control, Defense Secretary Donald Rumsfeld said Sunday.

Because of that, U.S. military officers in the field continue to appeal by satellite phone, covert radio broadcasts and leaflets for the surrender of both commanders of individual Iraqi military units, and higher-ranking military officials.

The effort aims both to speed Iraq's overall surrender, lessening bloodshed, and to help in the search for weapons of mass destruction, Rumsfeld and other officials said.

"We have received reports from various prisoners that have given us leads," in finding chemical and biological weapons, Lt. Gen. John Abizaid said Sunday, mentioning in particular the two Iraqi generals.

But finding Saddam's well-hidden chemical weapons caches could take a long time, even if Iraqi soldiers and officers provide clues, Abizaid warned.

The U.S. government believes only a handful of top Iraqi officials know full details of Saddam's chemical and biological weapons programs, and that the regime had years to find sophisticated hiding places for them.

Rumsfeld predicted, on CBS' Face the Nation, that Republican Guard units might begin to surrender as U.S. forces move closer to the units' locations guarding Baghdad.

U.S. military officers in the field are in contact with many military commanders through satellite phones and other means, including some Republican Guard unit leaders. But no Republican Guard units have yet surrendered, Rumsfeld said.

The vast majority of the 2,000 Iraqi POWs are regular army soldiers captured in the south who have next-to-no valuable information for American officials, said Daniel Goure, a military analyst at the Lexington Institute in Washington.

The only exceptions might be the commander of the 51st Infantry Division who surrendered in the south and any specialized communications or engineering soldiers.

The most important POWs so far -- in addition to the two generals -- probably are those captured by U.S. special operations forces, working in secrecy, who have seized at least one airfield in western Iraq, said Goure and other outside military experts.

Those airfields probably would have been used to launch any missiles at countries like Israel, and thus might contain information pointing to where the Iraqi regime stored chemical weapons or how it planned to move them to missile sites.

Any documents seized at such sites might contain valuable information such as when chemical weapons parts were scheduled to arrive or alternative deployment sites, Goure said.

Officers at those sites also might know details of chemical weapons plans. But even those officers might know only scattered, fragmentary details of where weapons were stored before the war began -- and not where they are now, Goure said.

U.S. military teams are urgently examining a large cache of documents uncovered by special operations forces at one such site after a firefight in western Iraq on Saturday night, Gen. Richard B. Myers, chairman of the Joint Chiefs of Staff, said Sunday on ABC's This Week.

U.S. officials believe that commanders in the field in some locations had the authority to launch biological or chemical weapon attacks, Rumsfeld said, adding urgency to the search.

He warned again that any Iraqi in charge of biological or chemical weapons should give up, rather than carry out an order to launch a deadly missile -- or face U.S. wrath.

"The important thing to remember is Saddam Hussein cannot use weapons -- chemical or biological weapons. He has to get other people to do it for him. And we have to persuade them that they best not do it," Rumsfeld said.

Abizaid said the search may be long.

"I think we'll find weapons of mass destruction once we have had an opportunity to occupy Baghdad, stabilize Iraq, talk to Iraqis that have participated in the hiding and the development of it," the general said. "You shouldn't think it's going to happen tomorrow."