America West Airlines yesterday asked the Department of Transportation to reapportion the landing and departure rights at Washington National and La Guardia airports at the expense of carriers that now dominate those terminals.

The two high-density airports are among a handful where traffic is limited by the Federal Aviation Administration. As a result, an airline cannot provide service to them unless it obtains a "slot" from a carrier that has one.

America West, a regional airline with headquarters in Phoenix, wants to expand its service in the East, including flights to National and La Guardia, in New York. The airline said that it has been blocked because there are no slots available at those airports at reasonable hours.

As a result, the airline asked the DOT to repeat an earlier move: take away slots from the "have" airlines and put them up for grabs by the "have-nots." According to America West, such action is warranted because airline industry mergers have concentrated nearly half of the slots at the two airports in the hands of two companies, Texas Air Corp. and USAir Inc.

If USAir's proposed acquisition of Piedmont Aviation Inc. is approved, "these levels of concentration will become staggering, with Texas Air and USAir controlling more than 50 percent of the air carrier slots at each airport," attorneys for America West said in a filing with DOT.

America West raised the same point when it argued against approval of the USAir-Piedmont merger.

USAir responded that America West could serve the same markets by flying into other airports, such as Dulles and Newark, where access is less restricted. If the merger is approved, USAir will have 20 percent of the slots at La Guardia -- where Texas Air (which is the parent company for Continental Airlines and Eastern Air Lines )has 25 percent -- and 24 percent of the slots at National, where Texas Air has 27 percent, USAir's filing said.

According to USAir, DOT has determined that those levels of concentration are not a competitive concern.

USAir also said that "America West could well afford to buy slots at Washington National or La Guardia to compete at these airports." However, America West asserted in its filing that slots at desirable hours were not available at any price.

Allocating slots at high-density airports is a perennial problem for federal transportation officials. In 1985, DOT turned over slots to carriers that already had them at no cost and subsequently gave them the right to buy, sell and trade slots. In addition, DOT instituted a rule that returns slots that are unused to the FAA, which disposes of them in a lottery.