Safety for passengers and crews could be compromised, they say.
The situation got bad enough three years ago, even before the latest surge in fuel prices, that NASA sent a safety alert to federal aviation officials.
Since then, pilots, flight dispatchers and others have continued to sound off with their own warnings, yet the Federal Aviation Administration says there is no reason to order airlines to back off their effort to keep fuel loads to a minimum.
''We can't dabble in the business policies or the personnel policies of an airline,'' said FAA spokesman Les Dorr. He said there was no indication safety regulations were being violated.
The September 2005 safety alert was issued by NASA's confidential Aviation Safety Reporting System, which allows air crews to report safety problems without fear their names will be disclosed.
''What we found was that because they carried less fuel on the airplane, they were getting into situations where they had to tell air traffic control, 'I need to get on the ground,' '' said Linda Connell, director of the NASA reporting system.
With fuel prices now their biggest cost, airlines are aggressively enforcing new policies intended to reduce consumption.
In March, for example, an airline pilot told NASA he landed his regional jet with less fuel than required by FAA regulations. ''Looking back,'' he said, ''I would have liked more gas yesterday.'' He also complained that his airline was ''ranking'' captains according to who landed with the least amount.
A month earlier, a Boeing 747 captain reported running low on fuel after meeting strong headwinds crossing the Atlantic en route to John F. Kennedy International Airport in New York. He said he wanted to stop to add fuel but continued on to Kennedy after consulting his airline's operations manager, who told him there was adequate fuel aboard the jet.
When the plane arrived at Kennedy, the captain said it had so little fuel that had there been any delay in landing, ''I would have had to declare a fuel emergency'' - a term that tells air traffic controllers a plane needs immediate priority to land.
The last major U.S. air crash attributed to low fuel was on Jan. 25, 1990, when an Avianca Boeing 707 ran out while waiting to land at Kennedy. Seventy-three of 158 aboard were killed.