The move by the U.S. Public Interest Research Group and the Aviation Consumer Action Project to join the recently formed Coalition for an Airline Passengers' Bill of Rights came on the same day the Senate Commerce Committee held a hearing in Washington, D.C., to discuss proposed passenger rights legislation.

The legislation, offered by Sen. Barbara Boxer, D-Calif., and Sen. Olympia Snowe, R-Maine, would give passengers the option of leaving a plane grounded for three hours, as well as require airlines to provide food, potable water and adequate bathroom facilities.

''We've had air service for over 100 years, and we still don't treat passengers right,'' Ed Mierzwinski, PIRG's consumer program director, said during a teleconference with reporters before the committee hearing. ''The excuses they [airlines] make'' for poor service ''are weak,'' Mierzwinski added.

Paul Hudson, executive director of the Aviation Consumer Action Project, said part of the problem is ''chronic congestion'' at airports and aboard planes. ''What we have now is involuntary imprisonment, which can last 10 or 11 hours,'' Hudson said during the same teleconference.

The two were joining an effort started in January by real estate agent Kate Hanni of Napa Valley, Calif. In late December, Hanni, 46, was stuck aboard an American Airlines flight grounded at the airport in Austin, Texas, for about nine hours. Hanni, who founded the Coalition for an Airline Passengers' Bill of Rights and is now its president, helped persuade Boxer and Snowe to draft the legislation.

But the passengers' rights effort gained considerable momentum in mid-February, when JetBlue Airways canceled about 1,000 flights during a six-day period after an ice and snow storm on Valentine's Day. The uproar caused by the stranding of about 130,000 passengers, most of them at New York's John F. Kennedy airport, forced JetBlue Chairman and founder David Neeleman to make several public apologies. JetBlue also issued its own ''bill of rights,'' saying it would allow passengers off a plane that has been on the ground for 5 hours.

But David Castelveter, a spokesman for the Air Transport Association, which represents the major carriers, said the industry opposes legislation to deal with the problems.

''We think if you mandatorily impose inflexible standards, it will create greater inconvenience for customers,'' Castelveter said. He said lengthy delays such as occurred at Kennedy and Austin, are rare. ''But when there's [bad] weather, there's often not much that can be done,'' Castelveter said.

Several congressional aides said Wednesday they were not certain the Boxer-Snowe bill would come to a vote this year. But David Snepp, a spokesman for Snowe, said he believed the bill has ''a strong chance'' of getting to the floor, partly because of the nationwide headlines garnered by the JetBlue Valentine's Day meltdown.