Under pressure from the Department of Transportation, six of the nation's biggest airlines yesterday agreed to attempt to reduce delays for most of their flights or face fines from the federal government.

In the strongest action to date to combat the recent epidemic of airline delays, the Department of Transportation got the carriers to sign consent agreements under which they promised to modify their schedules at four of the nation's busiest airports so that their flights will arrive or depart within 30 minutes of their published schedules at least 75 percent of the time by next April 1.

The penalty for consistently late flights will be up to $1,000 per flight per day, according to a DOT spokesman.

The airlines agreeing to the stipulation are American, Delta, United, USAir, Continental and Eastern. The agreements involve flights by those airlines into or out of Atlanta's Hartsfield, Dallas-Fort Worth, Chicago O'Hare and Boston's Logan airports.

"The American people have a right to truth in airline scheduling," Transportation Secretary Elizabeth Hanford Dole said in a statement. "I commend American, Delta, USAir, United, Continental and Eastern for their willingness to work with the department in concluding these agreements and improving their on-time performance, thus providing better service to their passengers."

A Federal Aviation Administration study found that airline delays increased 25 percent last year. Some flights at the four airports covered under the agreements are 15 minutes or more late 70 percent of the time, according to the FAA.

The problem has been traced in part to airline schedules that concentrate a large number of flights at particular times of the day. The DOT has been attempting for months to get airlines to voluntarily change their schedules, but apparently has not been satisfied with the progress of that effort.

Dole wrote to the six airlines earlier this month to request that they sign agreements regulating schedules and delays on all flights. The airlines and the department then negotiated a compromise limiting the action to the four airports. Given the number of airlines and the importance of the airports involved, the agreements likely will affect a majority of the nation's scheduled air service.

Under the agreements, the six airlines are to modify their schedules so that at least half their flights to and from those four airports operate within 30 minutes of scheduled times by Nov. 1. The requirement increases to 75 percent April 1. Allowances will be made for flights that are delayed by weather and equipment problems, according to a DOT spokesman. "This is focused on flights that are chronically late," he said.

The spokesman said the department might attempt to extend the agreements to other airlines and airports in coming months. airlines and these four airports are only part of a broader investigation," he said. "There are only six agreements at this point. There are other airlines that are being looked at." He declined to identify the airlines, but the DOT has said it is also investigating flight delays at Newark, New York's La Guardia, Denver's Stapleton and San Francisco International airports.

the agreements, such as Delta, praised them as a boon to the industry. Delta said the action "should be instrumental in further reducing delays in the operation of airline flights."

But other airlines, including Eastern, said they were not pleased by the DOT's tactics in forcing them to sign consent agreements.

"Eastern signed, but we believe that this was a very poor example of the governmental process in action," the Miami-based airline said in a statement. "We were presented with a fait accompli this afternoon. That is no way to run a delicate and sensitive industry. We have definite and serious reservations about the actions taken today."

A spokesman for American Airlines, speaking before the DOT agreements were announced, said the airline felt it had done enough voluntarily to reduce its delays in recent months, and added, "It's really difficult for us to see this {proposal} on the table when we feel we've put forth a tremendously good faith effort. ... It really is frustrating when you've done this much and gone this far to be presented with a decree like this, which seems completely arbitrary."

But Continental Airlines, which like Eastern is owned by Texas Air Corp., said, "We're not sure that {the DOT system of deadlines and fines} process is the right way to get the job done. But the public's right to an efficient on-time airline system is so important, we're willing to give it a try."