WASHINGTON — Several Supreme Court justices expressed strong doubts today about extending the reach of American courts into Iraq to stop the transfer of two American citizens into Iraqi control.

The skepticism by Chief Justice Roberts and others came today after a lawyer representing the Bush administration argued that American courts are powerless to intervene in the cases of Mohammad Munaf and Shawqi Omar.

Mr. Omar allegedly assisted a terrorist network and Mr. Munaf allegedly set up the 2005 kidnapping of three Romanian journalists in Baghdad. Both proclaim their innocence and both are Sunni Muslims who say they will be tortured if turned over to the Iraqi government.

The Bush administration’s legal position is that the two men are being held by the multinational force in Iraq, of which the American contingent is only a part.

The lawyer for Messrs. Omar and Munaf, Joseph Margulies, says the two are in the control of the American military and should have access to American courts.

Mr. Margulies told the justices that “the buck stops with the United States government when it comes to these detainees.”

The chief justice pointed out that the American military in Iraq has thousands of foreign nationals under its control, raising the possibility that by Mr. Margulies’ logic, they also should be given access to American courts.

But they aren’t American citizens, Mr. Margulies replied.

A deputy Solicitor General, Gregory Garre, said 20,000 people are in custody in Iraq and that 2,000 of them have been transferred to Iraqi control.

Responding to concerns expressed by Justice Alito, Mr. Margulies said providing Messrs. Munaf and Omar the rights to which they are entitled as American citizens would not impact the other 20,000 people in custody in Iraq.

“There is no floodgates problem” because of their citizenship and other safeguards, said Mr. Margulies.