As 55 Americans were welcomed home from what could be the last of the "freedom flights" from Iraq and Kuwait, the State Department expressed concern yesterday for the safety of 900 U.S. citizens still stranded in those countries.

Most of the unspecified number of American men still trapped have gone into hiding, and the Iraqis have begun detaining Americans with health problems to use as human shields against any possible U.S attack, said spokesman Margaret Tutwiler.

Describing the Iraqi action as "deplorable," Tutwiler said Iraqi President Saddam Hussein was denying repeated U.S. demands for "immediate evacuation" of 69 Americans who needed medical attention.

She said the Iraqis are also continuing the "barbaric practice" of detaining Americans at military bases to ward off a U.S. air strike and now hold 93 for that purpose.

One of the detainees has "serious medical problems," Tutwiler said. His detention is a "very disturbing development," she said.

"We find it particularly deplorable that the Iraqis have not only ignored our request to evacuate Americans with serious medical problems, but are now beginning to detain them," she said.

What U.S. officials said they fear may be the last Baghdad-sanctioned, U.S.-chartered evacuation flight left Iraq on Saturday with 55 U.S. citizens and 45 children and spouses on board. It arrived Sunday night at Raleigh-Durham airport in North Carolina after a stopover in London.

So far, 1,900 Americans and their foreign-born families have been airlifted out of the Persian Gulf, Tutwiler said. Five hundred more have escaped, according to a State Department source.

"We have no more charter flights scheduled at this time," Tutwiler said.

At least 900 U.S. citizens remain trapped, including 600 to 700 in Kuwait and 300 to 350 in Iraq, she said, but she refused to say how many had chosen to stay, arguing such information jeopardized the safety of those still trying to leave.

Those who decided to stay include Kuwaitis with young children who are U.S. citizens, said a source.

American men still in Iraq and Kuwait are "in hiding," Tutwiler said, but she refused to give numbers in case it "impaired the ability of those Americans to get out of the country."

"We don't want the Iraqis to know how many to go looking for," the source added.

Saddam said Sunday he would attack Saudi Arabia, other Arab countries and Israel if the United Nations sanctions imposed following Iraq's Aug. 2 invasion of Kuwait "strangled" his country.

But Tutwiler dismissed the threat as "another outlandish, outrageous statement."