WASHINGTON - President Bush surprised Congress by refusing to sign a defense authorization bill, in part because it could revive a lawsuit brought by American prisoners of war during the 1991 Persian Gulf War who say the Iraqis tortured them.

Their suit sought to establish the principle that war prisoners tortured in violation of the Geneva Convention were entitled to sue the country that tortured them.

By keeping the bill from becoming law, Bush delayed pay raises for the troops and improvements in the care of wounded veterans. On Friday, he pointed to a little-noted provision in the huge bill that he said could trigger a wave of lawsuits that might "imperil billions of dollars of Iraqi assets."

But he did not say that the main lawsuit that had drawn the attention of the White House and the Iraqis was a claim from American prisoners of war.

The 17 ex-POWs, most of them pilots who had been shot down, sued Saddam Hussein's regime for their brutal treatment after their capture. Among them was Navy aviator Jeffrey Zaun of Cherry Hill.

In 1996, Congress partly waived the rule that shields foreign countries from being sued. After hearing evidence of how the former POWs had been beaten and starved, a judge awarded them a total judgment of $959 million.

But that verdict came shortly after the United States had invaded Iraq and toppled Hussein. Bush administration lawyers then intervened in the case and said the judgment should be thrown out.

The move rankled some military and veterans groups.

"It seems so strange to have our country fighting us on this," said retired Air Force Col. David W. Eberly, who was the senior officer among the former POWs.

But a U.S. appeals court agreed with the administration and overturned the verdict. The judges ruled that individuals were not entitled to sue foreign governments for torture and abuse, despite the 1996 law. The case appeared to be at an end two years ago when the Supreme Court refused to hear an appeal from the ex-POWs.

"What message do we send for the future" if war prisoners can be tortured with impunity? Lt. Col. Clifford Acree asked at the time. A pilot in 1991, he was shot down by a surface-to-air missile on the first day of the Persian Gulf War and was blindfolded and beaten after he was taken captive. He later served as the lead plaintiff in the suit.

But this fall, Sen. Frank R. Lautenberg (D., N.J.) won an amendment to the Defense Department bill making clear that individuals who were victims of state-sponsored torture or other human-rights violations could sue for damages. The measure, broadly supported by Republicans and Democrats, would also allow such claims to be revived if they were dismissed earlier.

"My bill would provide victims of state-sponsored terrorism the justice they deserve," Lautenberg said.

Even though Lautenberg said his measure was targeted at Iran and Libya, Bush said Friday that he would not sign the bill because of the possible effect on Iraq. He did not mention the Gulf War POWs directly, though he referred to their case.

Bush described the new provision as being "contrary to international legal norms." If signed into law, it "would expose Iraq to new liability of at least several billion dollars," Bush said in his disapproval message. It "would attempt to revive a $959 million judgment against the new democratic government of Iraq based on the misdeeds of the Saddam Hussein regime."

Moreover, he said, the new law could trigger similar suits against the United States.

White House spokesman Tony Fratto said Bush's concern went well beyond the case of the Gulf War POWs: "Really, the concern is the accumulation of all the potential cases that could really cripple Iraq if they [plaintiffs and their lawyers] could enforce liens against assets."

Attorneys who represented the ex-POWs said in 2005 that they did not expect to collect the $959 million judgment. But they said they hoped the U.S. government would help them negotiate a settlement for a much smaller amount.