Some airline pilots would fly fewer hours and others would fly longer under proposed rules to help prevent dangerous fatigue, transportation and labor officials said Friday.

The proposal would set different requirements based on the time of day, number of scheduled flight segments, flight types, time zones and likelihood that a pilot is able to get enough sleep, Transportation Secretary Ray LaHood said in his blog. The proposal is being released Friday.

It would also require that pilots be given nine hours of rest between work days, an increase of an hour over current rules.

Pilots have complained that the current eight-hour rest period often results in only a few hours sleep. The period begins as soon as pilots leave the plane. They still have to leave the airport, check into a hotel, prepare for bed and then rise early enough to dress, eat and be on time for the next flight.

The proposal is an attempt to prevent tired pilots from making errors that can cause crashes. It would update decades-old rules governing pilot work schedules with more flexible, scientifically based standards.

However, an increase in work hours for some pilots — a concept promoted by airlines — is likely to draw opposition from pilot unions.

LaHood called the proposal “a significant improvement in air travel safety.”

The Air Transport Association, which represents major airlines and cargo carriers, said in a statement that it supports “pilot-rest and fatigue-management rules that are science-based, effective and crafted to truly improve safety.”

“We will be evaluating the FAA pilot-fatigue rule against that standard and will be guided accordingly,” the statement said.

It will be at least months before the proposal is made final. FAA and the Transportation Department have been working on the proposal for the past 15 months. The impetus for the new rules was the crash of Continental Connection Flight 3407 near Buffalo, N.Y., in February 2009. A National Transportation Safety Board investigation found that both pilots on the flight were probably suffering from fatigue, although fatigue wasn’t a direct cause of the accident.

Finding ways to prevent pilot fatigue has stymied federal regulators and the airline industry for decades. The NTSB has been urging since 1990 that rules be updated to reflect fatigue research.

The FAA proposed new rules in the late 1990s. The proposal lingered for more than a decade without further action, and agency officials cited an impasse between pilots and industry. The proposal was withdrawn last year when the agency began working on the issue again.