WASHINGTON -- The war on terrorism gives the government power to seize Americans and hold them without charges for as long as it takes to ensure they are not a danger to the nation, the Bush administration told the Supreme Court on Wednesday.

Attorneys for two men detained by the government argued in reply that fighting terrorists cannot mean a president has unchecked authority to snatch U.S. citizens and hold them without a chance to plead their case.

"We could have people locked up all over the country tomorrow," said Frank Dunham, attorney for a Louisiana-born man captured while fighting with the Taliban in Afghanistan.

Two-and-a-half years after the Sept. 11, 2001, jetliner attacks that killed thousands, the nation's highest court considered far-reaching questions about civil liberties, law and America's security in a changed world. By their words in court, a majority of justices seemed to give at least qualified support to the Bush administration.

The justices heard two cases about U.S. citizens being held as "enemy combatants." Yaser Esam Hamdi was born in Baton Rouge while his Saudi father worked there, but grew up in the Middle East. Jose Padilla was born in Brooklyn and raised in Chicago.

The American-born men, like foreign fighters also labeled enemy combatants and held abroad, have been in near solitary confinement, without access to courts, lawyers or the outside world.

Only in the past month, with the Supreme Court about to hear their cases, have they been allowed to meet with lawyers.

"We've had war on our soil before, and never before in our nation's history has this court granted the president a blank check to do whatever he wants to American citizens," attorney Jennifer Martinez argued on behalf of Padilla, a former gang member and alleged al-Qaida associate arrested at O'Hare Airport on suspicion of plotting to detonate a radioactive bomb.

Government attorney Paul Clement countered that Congress gave the president broad power to go after terrorists and head off future threats at home or abroad. He likened Padilla to a "latter-day, citizen version of Mohammed Atta," ringleader of the Sept. 11, 2001, hijackings.

The open-ended detentions prevent the men from rejoining the fight against the United States and help the government gather intelligence, Clement told the justices. Prisoners of war in other conflicts haven't been able to challenge their detentions in court, he said.

"But have we ever had a situation like this where presumably this warlike status could last for 25 years, 50 years, whatever it is?" asked Justice Sandra Day O'Connor.

Any wartime detention can seem indefinite, at least at the start, Clement replied. "If you talk about a detainee in 1942, they're not going to know how long World War II is going to last."

Several justices suggested it is impractical, perhaps impossible, to expect the government to hold extensive hearings before holding someone -- even a citizen -- who it suspects is fighting for the enemy.

"You want them to run down the members of the Afghan allies who captured this man and get them to testify in a proceeding?" Justice Antonin Scalia asked Hamdi's lawyer. "It's just putting unreasonable demands upon a war situation."

Wednesday's back-to-back arguments were the last of the current Supreme Court term. The justices are expected to rule in the Hamdi and Padilla cases by July. Last week the court heard a similar case about legal rights of foreign enemy combatants held at Guantanamo Bay, Cuba, and that ruling is also expected by summer.

Taken together, the three cases give the court the opportunity to broadly define how the government may treat citizen and non-citizen terrorism suspects picked up at home and abroad.

Hamdi was captured on an Afghan battlefield weeks after the Sept. 11 attacks.

The government has presented no public evidence that Hamdi was a terrorist, and his lawyer told the justices that if the government had its way Hamdi would never get the chance to defend himself.

"We have never authorized detention of a citizen in this country without giving him an opportunity to be heard, to say, 'Hey, I am an innocent person,"' Dunham argued.

Speaking to reporters later, Dunham said he was not optimistic.

The Bush administration won its argument in a lower court in the Hamdi case, but lost a federal appeals court fight in the Padilla matter.

Representing the government in both cases Wednesday, Clement referred often to the congressional statute passed a week after the 2001 attacks that gave the president authority to use "necessary and appropriate" means to fight terrorism.

Justice Ruth Bader Ginsburg worried that a broad reading of the language could give a president unlimited power.

"What is it that would be a check against torture?" she asked.

Clement said that a U.S. president wouldn't do that.

But "what's constraining? That's the point," Ginsburg replied. "Is it just up to the good will of the executive? Is there any judicial check?"

Clement responded a president should have the authority to use his military powers to fight terrorism, without "judicial micromanaging."

Clement also argued that a federal court in New York improperly ruled in Padilla's favor because Padilla was being held in South Carolina. Padilla's lawyer was appointed in New York.

The cases are Hamdi v. Rumsfeld, 03-6696, and Rumsfeld v. Padilla, 03-1027.