Secretary of State James A. Baker III turned up the pressure on Saddam Hussein yesterday, accusing the Iraqi president of "making political and economic war" on U.S. citizens held hostage by Iraq and charging that Americans are becoming sick from serious mistreatment.

According to Baker, more than 100 Americans being held as "human shields" by Saddam "are forced to sleep on vermin-ridden concrete floors. They are kept in the dark during the day and moved only at night. They have had their meals cut to two a day. And many are becoming sick as they endure a terrible ordeal. The very idea of Americans being used as human shields is simply unconscionable."

In an address to the Los Angeles World Affairs Council, Baker also renewed the threat of military force in the confrontation with Iraq. "We will not rule out a possible use of force if Iraq continues to occupy Kuwait," Baker said.

Baker's complaint about the treatment of Western hostages was echoed by several of the more than 260 former French hostages who arrived in Paris last night. "It is especially hard for the Americans and the British hostages there, who are really being treated like prisoners of war," said Pierre Sanchez, one of the returning French captives.

Baker's speech was described by administration officials as part of an effort to refocus attention on Iraq after several weeks of budget politics and other diversions that some officials said may have led to doubts in Baghdad and other foreign capitals about American resolve.

Baker reiterated that the mission of the more than 200,000 U.S. troops in the Persian Gulf region is to defend Saudi Arabia, protect American lives and "to ensure the effective implementation" of the United Nations Security Council resolutions calling for Iraq to pull out of Kuwait.

Since the beginning of the crisis, the Bush administration has sought to avoid emphasizing the hostages' plight so they do not become the dominant factor in policy decisions. But officials said there was worry that mistreatment of the hostages had slipped from public view, and Baker's remarks were a deliberate effort to put their deteriorating situation squarely before the public again.

Officials added that Baker's remarks were meant to make clear to Saddam and to the American public that mistreatment of U.S. citizens could be a justification for military action against Iraq.

Thomas R. Pickering, the U.S. ambassador to the United Nations, said yesterday, "Every nation has a duty to protect its citizens. This is a fundamental obligation. The United States will do that which is necessary to meet its obligation to its own citizens."

State Department officials said Baker intended yesterday to go beyond previous descriptions of "atrocities" in Kuwait and Iraq, and provide specific, graphic evidence that Americans and others are being mistreated. He asserted that an Iraqi soldier at a checkpoint had killed two sick Kuwaiti children who were en route to a hospital, and that Iraqi troops used animals in the Kuwaiti zoo for target practice.

Baker said "life for those who have escaped Saddam's soldiers" in Kuwait is filled "with terror. Obtaining food and water -- the most basic of human necessities -- carries with it the risk of death."

He said diplomats at the besieged U.S. Embassy in Kuwait City, "are not giving in" even though supplies of food, water, and power have long been cut off.

In related developments, President Bush has summoned several dozen congressional leaders to the White House today to talk about the gulf crisis. Bush said yesterday he believes he has ample authority to act in the gulf without prior approval from Congress.

"History is replete with examples where the president has had to take action," Bush said. "And I've done this in the past and certainly . . . would have no hesitancy at all."

Bush said that despite the apparent failure of the diplomatic mission to Baghdad by Soviet President Mikhail Gorbachev's Mideast emissary, Yevgeny Primakov, he still sees hope for a peaceful resolution and possible negotiations once Iraq pulls out of Kuwait.

"If he {Saddam} gets out of Kuwait and restores the legitimate government, then there's a way to work out difficulties that may have existed," Bush said. "But we're not going to have any preconditions" for Iraqi withdrawal.

Baker, who departs later this week for the Persian Gulf and European capitals for consultations on the crisis, said the economic sanctions against Baghdad are gradually hurting the country.

"Every day, as the sun sets, Iraq gets weaker," Baker asserted. "Sooner or later, and we all hope sooner, even the Iraqi dictator is going to notice that he's in deep trouble and the trouble is getting deeper. Sooner or later, one way or another, Iraq is going to have to comply" with the U.N. resolutions, he said.

Officials said Baker's speech was intended to present the administration's case at a time when public opinion polls are showing growing doubts about the military deployment. Baker said "whatever the noise of the naysayers, our moral principles as well as our material interests make us a leader."

Baker's speech followed a weekend at his Wyoming ranch, where guests included Secretary of Defense Richard B. Cheney and Robert Teeter, a senior political adviser to Bush and the GOP. Aides to Baker and to Teeter said the weekend was long-planned and had nothing to do with the situation in the gulf or Bush's sinking public approval ratings.

"I can't tell you the three did not talk about the current political situation," said one aide, "but I can tell you this was put on before anyone knew there would be a budget stalemate or a gulf crisis."

Staff writers Ann Devroy and Dan Balz contributed to this report.