Up to 1,200 U.S. POWs were left behind when the Korean War ended in 1953, according to testimony at a House hearing Tuesday.

And more than 100 of them may have been subjected to gruesome medical experiments and then executed, witnesses told the subcommittee on military affairs.

Declassified government memos show that top U.S. officials, including President Dwight Eisenhower, knew about the reports that POWs were still being held in the North.

But the officials, fearful of touching off a nuclear holocaust in the tense Cold War 1950s, decided against pressing the issue.

Rep. Robert K. Dornan, R-Calif., who heads the subcommittee, accused the U.S. government of "writing off captured American fighting men after no-win stalemate wars" throughout the Cold War period.

North Korea has said it is not holding any Americans prisoner. A few U.S. soldiers who defected during the war still live in North Korea, committee investigator Al Santoli said.

Korean War Veterans Association president Nicholas Pappas said his 12,000- member group would push Congress to take follow-up action.

"You never want to leave people behind," Korean War veteran Dan Randall told WJLA-TV in Washington, D.C. "But you have to look at the big picture."

Retired Army colonel Phillip Corso, who was a National Security Council aide to Eisenhower, testified that 500 sick and wounded American prisoners were still being held within 10 miles of the site where the 1953 armistice was signed on the border between North and South Korea.

Corso said he confirmed later that two trains and possibly three, each carrying 450 American prisoners, were sent to the Soviet Union.

"Therefore, the final figure was confirmed 900, and 1,200 possibly," he testified. "These POWs were to be exploited for intelligence purposes and subsequently eliminated."

Czech defector Jan Sejna testified that about 100 American prisoners were shipped from North Korea through Czechoslovakia to the Soviet Union after the Korean War.

He said the Americans also were used to test mental and physical endurance and various mind-control drugs. Moscow ordered Czechoslovakia to build a hospital in North Korea for the experiments, Sejna said.

Dornan vowed to pursue the matter. "It's not the end of the issue," he said. "It's the first airing."