T'S easy to understand why taking a cruise is an attractive travel option for people with disabilities: an array of activities in one place, from spas to live music to casinos; no need to pack and unpack continually; a cabin at the ready for midday rest; even medical services on board. Some cruise ships offer services such as kidney dialysis, special devices for the hearing impaired or supplemental oxygen.

According to a survey conducted for the travel industry by Harris Interactive in 2002, 12 percent of people with disabilities had taken a cruise within the past five years - compared with 8 percent of the nondisabled population - and more than half of those who took one cruise promptly signed up for a second voyage.

But pick the wrong ship, and passengers with impaired mobility might find themselves on a floating obstacle course, lacking accessible public restrooms, lifts for the swimming pools and Jacuzzi baths, and adequately designed staterooms.

The question in a case argued before the Supreme Court last month was not whether such problems represent bad business judgment but whether disabled cruise passengers who encounter them have recourse to the Americans With Disabilities Act.

Title III of the federal statute, which prohibits "any place of public accommodation" from depriving individuals with disabilities of "the full and equal enjoyment" of "goods, services, facilities, privileges, advantages, or accommodation," has transformed the landscape in the 15 years since it became law. But cruise ships present a special issue. Nearly all of the ships that serve the United States market fly under foreign flags, and the question of whether the disability law applies to them has proven a particularly difficult one for the courts.

Although both the Justice Department and the Transportation Department have maintained that the law does apply to ships that enter United States waters, Congress itself was silent on the subject. Two federal courts with jurisdiction over some of the most active cruise ship ports - the 11th Circuit, covering Fort Lauderdale and Miami, and the Fifth Circuit, covering New Orleans and Houston - have reached opposite conclusions.

The confusion is not hard to understand. The issue pits two longstanding legal principles of maritime commerce against one another: the "law of the flag" versus the "peace of the port." Under the first, domestic law is not to be applied to foreign ships, out of respect for the sovereignty of their countries of registry. Under the second, a ship entering another country's waters takes on certain obligations under that country's laws.

The Supreme Court's own precedents look in both directions. In a Prohibition-era case involving the Cunard Line, the justices upheld the attorney general's position that foreign ships entering United States ports could not carry any liquor, even under lock and key. But in a 1963 case, the court ruled that federal labor law did not apply to labor relations on a foreign ship, even in United States waters.

The case the justices will decide within the next several months, Spector v. Norwegian Cruise Line Ltd., began as a class-action lawsuit under the Americans With Disabilities Act against the Norwegian Cruise Line, a subsidiary of Star Cruises, based in Malaysia. Norwegian keeps a Miami business office and serves a predominantly American cruise market. It registers its ships in the Bahamas.

The plaintiffs are three passengers with disabilities and two traveling companions, who booked cruises in 1998 and 1999 out of the port of Houston on two of the Norwegian Line's older ships, the Norwegian Sea and the Norwegian Star. According to their allegations, which remain unproven because the suit has not gone to trial, the plaintiffs were charged a premium for accessible staterooms that were in undesirable interior locations, had to make awkward trips back to their rooms because the public bathrooms were not accessible, faced many inaccessible doorways, and could not use the swimming pools or Jacuzzis due to the absence of hydraulic lifts.

While denying the charges, Norwegian Line argued that the Americans With Disabilities Act simply did not apply to its ships. The Fifth Circuit agreed, and ordered the lawsuit dismissed. Defending its position in the Supreme Court on Feb. 27, Norwegian was supported by the government of the Bahamas, the United States Chamber of Commerce and the International Council of Cruise Lines.

The federal government, meanwhile, supported the plaintiffs' appeal, as did the attorneys general of Texas and seven other states and two coalitions of disability-rights organizations. The Texas attorney general, Greg Abbott, uses a wheelchair himself.

The government's basic argument was that "the foreign-flag status of a cruise ship does not affect the authority of the United States to protect its citizens within United States territory," as its brief asserted.

The cruise line's basic argument was not that Congress could not extend the disabilities act to foreign ships, but that it should not be assumed to have done so in the absence of a "clear statement." During the argument, several justices expressed concern that this argument might leave American passengers stripped of other civil rights protections as well because Congress has not been explicit about applying other federal laws to cruise ships either.

If the plaintiffs win this round, their lawsuit will be reinstated and the case sent back to the Federal District Court in Houston for trial. Whether a trial would ever take place is anyone's guess. The Norwegian Line's brief, while maintaining its legal position, pointed out that the Norwegian Star had already left its fleet (it has been replaced by a new vessel of the same name) while the Norwegian Sea will be removed this summer. The line's newer ships are filled with innovations to accommodate passengers with special needs, Norwegian said.

Norwegian pointed out in its brief that it was acting "in response to competitive market dynamics in effect throughout the cruise industry." In other words, what the law itself might or might not accomplish, capitalism already has.