WASHINGTON (Reuters) - The government has failed in recent years to adequately investigate passenger complaints against airlines, a disclosure by a watchdog on Wednesday that further angered lawmakers weighing a consumer protection law for air travelers.

Calvin Scovel, the Transportation Department (DOT) inspector general, told senators at a Commerce Committee hearing on a streak of embarrassing airline service problems that the Bush administration has basically surrendered oversight to industry in crucial areas.

He said the DOT has focused on civil rights complaints but has been lax -- despite a previous warning about its shortcomings -- in pursuing other cases and holding carriers accountable for long delays, lost bags, misleading advertising, oversold flights, and not communicating with passengers.

"The (DOT) has not conducted on-site compliance reviews, relying instead on self-certifications and company-prepared reports submitted by the air carriers without supporting documentation," Scovel said.

Michael Reynolds, the deputy assistant secretary for aviation, said the agency was open to tougher enforcement and would work with Congress on any consumer legislation even though it preferred market-based solutions.

Scovel will issue a report this summer on service meltdowns by American Airlines and JetBlue Airways Corp. in Texas and New York in December and February. Those incidents, in addition to recent government reports showing worsening flight delays industry-wide and a sharp increase in mishandled baggage, have prompted congressional scrutiny.

The commerce panel is considering legislation that would force airlines to let passengers off planes during long delays and take other steps to ensure their comfort while waiting to take off or reach an airport gate. This would include drinkable water, food and adequate restroom facilities.

A rash of high-profile performance setbacks in 1999 also triggered congressional concern, but lawmaker intervention was averted when carriers promised to do better.

"We backed off. You put it in writing and you (the airlines) didn't live up to it," Barbara Boxer, a California Democrat and co-author of the leading Senate air traveler bill, told the industry's top lobbyist, James May.

"We're going to push this on every bill that we can to get this done because it isn't right, it isn't fair," Boxer said of continuing service problems.

May, chief executive of the Air Transport Association, said prescribing remedies would force airlines to accommodate a minority of passengers and could cause longer delays, more cancellations and other disruptions to a system that handles 20,000 flights per day.

"Airlines need the flexibility to deal with each delay situation individually to help ensure that the fewest people possible are inconvenienced," May said.