ASHINGTON, April 28 — The Bush administration yielded no ground before the Supreme Court on Wednesday in arguing that the open-ended military detention of United States citizens as enemy combatants, without criminal charges or access to lawyers, was justified both in law and as policy.

It is "remarkable that we have to confront this question when our troops are still on the ground in Afghanistan," Paul D. Clement, principal deputy solicitor general, told the justices.

A majority of the justices expressed some degree of concern over the breadth of the administration's position. Justice Sandra Day O'Connor asked Mr. Clement why "a neutral decision maker of some kind" could not be provided to determine whether a detainee is being properly held. "Is that so extreme that it should not be required?" she asked.

Mr. Clement said the potential detainees' initial screening, sorting those to be held from those who need not be, met that requirement. "For all intents and purposes, that is a neutral decision maker," he said.

Mr. Clement also rebutted a suggestion by Justice Ruth Bader Ginsburg that detainees should have a forum to explain themselves. They already have one, he said, adding, "The interrogation process itself provides an opportunity for an individual to explain that this has all been a mistake."

Despite the justices' evident discomfort, it was far from clear by the end of two hours of intense and sober argument that the court would tell the administration that it had gone too far, either in the case of Yaser Esam Hamdi, an American-born Saudi who was seized in Afghanistan, or Jose Padilla, a Chicagoan taken into custody at O'Hare Airport.

In a case they heard last week, the justices appeared sympathetic to the argument that federal courts have jurisdiction to review the open-ended detention of noncitizens at the naval base at Guantánamo Bay, Cuba. The cases on Wednesday appeared to raise a more difficult issue: not only whether the detainees can get into court, but how the courts are to balance the rights they claim against the needs of national security that the government asserts.

Mr. Hamdi and Mr. Padilla, now in a brig in Charleston, S.C., have spent two years in military custody. Several justices questioned the open-ended nature of the detention.

"Doesn't the court have some business intervening at some point if it's the Hundred Years' War or something?" Justice Stephen G. Breyer asked.

Mr. Clement replied, "I'm not quite sure what you have in mind that they would intervene on."

Justice Anthony M. Kennedy, whose position appeared most in doubt, pressed Mr. Clement at one point for some sign of a concession. "I'm taking away from the argument the impression, and please correct me if I'm wrong, that you think there is a continuing role for the courts to examine the reasonableness of the period of detention," he said in a hopeful tone.

Mr. Clement was quick to correct him. "Well, I wouldn't take that away, Justice Kennedy," he said.

The outcome in both cases may well turn on how the court interprets the resolution Congress passed a week after the attacks of Sept. 11, 2001, authorizing the president to use "all necessary and appropriate force" against organizations or "persons" involved in planning the attacks or aiding the terrorists. If the detention of citizens requires Congressional authorization, Mr. Clement said, that resolution provided it.

"To read it to deny the government the authority to detain a latter-day citizen version of Mohammed Atta is to simply ignore the will of Congress," he said, comparing Mr. Padilla to a chief Sept. 11 hijacker.

The lawyer and Justice Breyer sparred over the meaning of the phrase "necessary and appropriate." To Justice Breyer, those words provide a basis for curtailing discretion. He asked why military detention was "necessary and appropriate in a country that has its courts open, that has regular criminal proceedings, that has all the possibility of adjudicating a claim that `I'm the wrong person.' "

He added, "Why is it a `necessary and appropriate' thing to do once you have such a person who is a citizen in this country to proceed by other than a normal court procedure?"

To Mr. Clement, the phrase was a commitment to presidential authority rather than a limit. "I certainly wouldn't read the Authorization of Force's use of the term `necessary and appropriate' as an invitation for judicial management of the executive's war-making power," he said, adding, "I would have viewed it as a delegation to the executive to use its traditional authority to make discretionary judgments in finding what is the necessary appropriate force."

Mr. Clement asked the court to recognize that "where the government is on a war footing, you have to trust the executive to make the kind of quintessential military judgments that are involved in things like that."

Jennifer Martinez, a Stanford Law School professor representing Mr. Padilla, and Frank W. Dunham Jr., a federal public defender representing Mr. Hamdi, reportedly captured on an Afghan battlefield with the Taliban, vigorously disputed the meaning Mr. Clement attached to the Congressional resolution. Ms. Martinez said authorizations to use force in wartime, even broadly written, have not "traditionally been interpreted to allow the executive unlimited power over citizens."

To Justice O'Connor's comment that "it appears to allow detention of people captured," Mr. Dunham replied that the resolution spoke only of military force and "does not have the word detention anywhere in it."

Mr. Dunham said if the resolution was interpreted to authorize "indefinite executive detention" at the president's discretion, "we could have people locked up all over the country tomorrow without any due process, without any opportunity to be heard."

He added, `'There is no indication that Congress intended any such thing."

The two cases, Hamdi v. Rumsfeld, No. 03-6696, and Rumsfeld v. Padilla, No. 03-1027, followed different routes to the court.

Mr. Dunham appealed a ruling by the United States Court of Appeals for the Fourth Circuit, in Richmond. That court ruled that although Mr. Hamdi was entitled to challenge his detention by means of a petition for a writ of habeas corpus, he was not entitled to contest the government's assertion of the basis for his classification as an enemy combatant, in a nine-paragraph statement by a Pentagon official, Michael H. Mobbs. In dismissing Mr. Hamdi's petition, the appeals court said Mr. Mobbs's statement provided all the justification the government needed.

In answer to a question from Justice John Paul Stevens, Mr. Dunham said although there was a "substantial dispute" about the validity of the government's assertions, he could not provide any details. Although he had recently been allowed to meet Mr. Hamdi for the first time, he said, "everything he has told me they tell me is classified, so I'm not allowed to convey it to the court this morning."

In the case of Mr. Padilla, said by the government to have plotted detonating a "dirty" radiological bomb, the administration brought the Supreme Court appeal. The United States Court of Appeals for the Second Circuit, in New York, ruled that the president was without authority to detain Mr. Padilla. The court cited a law Congress passed in 1971 to prohibit the detention of citizens without explicit authorization by Congress. The resolution authorizing military force after Sept. 11 did not provide that authority, the appeals court said.

The administration is arguing that the 1971 law, known as Section 4001, does not apply at all in the military context. But in any event, Mr. Clement argued, the appeals court decision should be overturned because by the time Mr. Padilla filed his habeas corpus petition, he was in military custody in the Fourth Circuit and was outside the Second Circuit jurisdiction.

If the Supreme Court rules for the government on that basis — a distinct possibility — the decision would shed no light on the deeper issues the case raises.