SAN FRANCISCO – To many people, the identification check may be the least of the indignities involved in getting on an airplane, a process that can include shedding much of one’s clothing and being, in essence, felt up by a federal security agent.

However, the 9th Circuit Court of Appeals heard arguments yesterday in a case brought by a California entrepreneur who says the demand for ID, which was instituted after the September 11, 2001, terrorist attacks, tears at the heart of what makes America free.

“I was taught in school that societies that require travel papers are totalitarian,” the plaintiff in the case, John Gilmore, 50, said yesterday. “I still believe that.”

Mr. Gilmore’s attorney, James Harrison, urged a three-judge panel yesterday to reinstate the lawsuit, which was thrown out last year by a federal district judge.

“One of the greatest dangers we have in the war on terror is what we do to ourselves,” Mr. Harrison said. He said the passenger ID rules violate the Constitution’s guarantees against unreasonable searches and burden the right to travel and to petition the government.

A Justice Department lawyer, Joshua Waldman, said the practice of checking IDs gives Americans more freedom. “It promotes the right to travel by protecting everyone’s safety,” Mr. Waldman said.

The most contentious issue in the case thus far has been the government’s refusal to disclose the Transportation Security Administration policy that sets identification requirements for airlines. The Justice Department offered to file a copy of the secret directive with the appeals court under seal. Mr. Gilmore’s lawyers and news organizations objected to that procedure, and the court declined to accept the filing.

Mr. Waldman told the judges yesterday that he “couldn’t confirm or deny the existence” of the order. He said it is not classified, but is considered “sensitive security information” that cannot be disclosed publicly.

“This is America. We do not have secret laws,” Mr. Harrison thundered. He also said Americans would be “floored” to learn that official airport signs that say identification must be shown don’t acknowledge that there are exceptions to the rule.

Each of the three judges on the appeal, Thomas Nelson, Richard Paez, and Stephen Trott, raised questions about the secrecy surrounding the security directive.

Under questioning by Judge Paez, Mr. Harrison conceded that the courts have not found a right to travel specifically by airplane. However, the attorney said the law still requires a judge to hear evidence about the ID requirement and to determine if it is reasonable.

Judge Trott noted that passengers are free to walk away from the security checkpoint. “It seems to me that without a seizure, simply asking someone for identification doesn’t implicate the Fourth Amendment at all,” the judge said. “It’s an inquiry. It isn’t a search.”

Much of the argument revolved around the arcane question of whether the case should have been filed with the appeals court at the outset because it involves a challenge to federal aviation regulations.

When Mr. Waldman said that the case belongs with the appeals judges, Judge Trott bellowed, “I love it. The government is clamoring to get before the 9th Circuit Court of Appeals. Be careful what you wish for.” The Justice Department often tries to keep disputes out of the 9th Circuit, which is widely viewed as the nation’s most liberal federal appeals court.

Mr. Gilmore’s lawsuit stems from a July 4, 2002, incident in which he sought to catch a Southwest Airlines flight from Oakland, Calif. to Baltimore. After refusing to provide identification, he was allowed to pass through security, but airline personnel later denied him permission to board. He also was rebuffed from taking a United Airlines flight.

Mr. Gilmore told reporters yesterday that he has not flown domestically since September 11, 2001, and also eschews Amtrak because of its ID requirement. Mr. Gilmore, a multimillionaire, said he recently traveled from San Francisco to Oregon by Greyhound bus after learning that the company no longer requires ID from passengers. “It felt like a little breath of freedom,” he said.

In 2003, Mr. Gilmore was ejected from a British Airways flight to London for refusing to remove a small button that said, “Suspected Terrorist.”

None of the arguments yesterday addressed whether the ID-checking procedure is effective at preventing terrorism. Mr. Harrison said that issue will be explored if the appeals court allows the case to go forward.

Mr. Waldman noted that the requirement to show identification is now commonplace, including at the federal courthouse where the appeal was argued yesterday. Mr. Gilmore said he was unwilling to show identification to enter the court building, but that guards admitted him after his attorney vouched for him.