The nation's airlines, recognizing that new airports or major expansion of existing ones are unlikely prospects, have developed a $240 million program of runway and electronic guidance improvements that they say will ease significantly flight delays and capacity problems.

The proposal, released yesterday by the Air Transport Association, is scheduled to be presented to Federal Aviation Administrator Donald D. Engen next week. The ATA, the major airline industry group, has lined up support from most other aviation interests.

Proposed are specific improvements at 22 airports. The airports, including Washington National, represent 60 percent of total passenger boardings, 50 percent of airline flights, 70 percent of airline cargo and 95 percent of airline schedule delays, according to James T. Murphy, the ATA's vice president for airports.

New runways are planned or under way at four of the airports: Dallas/Fort Worth, Kansas City, Houston and Denver. The Denver project has considerable political and environmental hurdles to clear.

"We realize that there is very limited opportunity for major additions like big new runways," Murphy said. "So all kinds of airline people took a concentrated look at each airport and came up with a bunch of little things that help a lot."

The congressional Office of Technology Assessment arrived at the same conclusion in a study last summer, finding that the opportunities for airport expansion were slight because of financial and environmental concerns. The OTA said better use of existing facilities would be required to help ease a capacity problem at major terminals.

The ATA program proposes $150 million in additional concrete and $90 million for added electronic guidance systems.

The concrete in most cases would extend and connect taxiways and parking ramps to provide more room at an existing airport or to improve traffic flow around runways. At National Airport, for example, the proposed improvements are to rehabilitate concrete aprons and strengthen taxiways.

Electronic guidance systems permit airplanes to take off and land in low-visibility weather. At the 22 airports, there are a total of 152 runway ends, but only 24 have high-quality instrument landing systems (ILS).

An ILS is placed on the runway most often used. But in bad weather, wind shifts force landings to other runways, where there often is no ILS. The ATA wants to install 24 new ILS systems and to upgrade 10 existing ILS systems.

The FAA has been slow to install new ILS in recent years because it hopes to replace the ILS with new technology electronic guidance.

A variety of federal, state and local financing systems already are in place to pay for many of the proposed improvements.

Most of the money comes out of airline passengers' pockets in the form of an 8 percent federal ticket tax. Individual airports can finance improvement bonds through landing fees.