Carriers serving the trans-Pacific air cargo market have decided against traditional April rate increases, saying the combination of overcapacity and weak traffic demand won't sustain price hikes.

Their decisions mean that rates in the market will have stayed flat for 12 months and send a signal that worldwide recessionary pressures have yet to subside, industry executives say.Generally, trans-Pacific air rates are revised each April and October. But rates remained unchanged through the autumn period as well.

For shippers, the rate outlook is positive, said Greg Smith, vice president of Colography Group, a consulting firm based in Marietta, Ga.

Mr. Smith said the trend toward smaller-size shipments, combined with larger bellies in modern-day passenger planes, translates into more freight moving in cheaply priced lower decks instead of high-cost freighters.

"You've got a buyer's market for a considerable period of time to come," he said.

With the exception of Federal Express Corp., which said it may raise some of its express rates slightly this spring on freight bound for Asia, airline executives interviewed for this story say no price increases are expected any time soon.

"We've looked at it, and we feel this is the way to go," said E.T. (Buz) Whalen, staff vice president of freight and mail for Japan Airlines. JAL has long been considered the rate trend setter across the Pacific.

Nippon Cargo Airlines is still studying the situation but is unlikely to adopt a rate increase, said Peter M. Diefenbach, marketing manager for the airline's U.S. division. "We haven't decided, but it doesn't appear the market is ready for an increase," Mr. Diefenbach said. "It probably wouldn't stick."

United Parcel Service also will maintain the status quo on rates, even though the Asian air freight market is the fastest-growing part of its overall business.

Ken Sternad, a UPS spokesman, said the company probably could raise rates over the short term, but the move might alienate a customer base that UPS has spent much time trying to cultivate.

Malaysian Airlines System is holding rates steady as well.

"We feel our rates are excellent right now," said Greg Himoff, cargo manager at the airline's New York terminal. "We want to remain competitive."

Carrier executives say the market continues to be plagued by what has become an all-too-common malady: too much aircraft capacity chasing too little freight. Soft demand for key export commodities such as beef and cotton out of Australia and New Zealand have aggravated the problem, observers said.

The situation is hardly helped by a decline in air exports from Japan. Mr. Whalen called exports from his country "extremely weak." William J. Razzouk, senior vice president of sales and customer service for Federal Express, said Asian export business was down by as much as 30 percent through winter. He's seen an uptick in recent weeks, however.

Japanese air export tonnage in December was off 3.3 percent from December 1990 figures, according to Global Aviation Associates, a Washington-based consulting firm. Imports into Japan fell 1.6 percent over the same period.

The numbers may be skewed due to the deployment of the Civil Reserve Air Fleet, which took a number of freighters out of commercial service and may have resulted in backlogs during that time.

Carriers will be buoyed by the annual spring surge in perishable exports such as fruits and vegetables. But that business is seasonal in nature, and executives say they've yet to see a strong, sustained pick-up in shipping activity, especially out of Asia.

"We're encouraged but not wildly optimistic," Mr. Razzouk said.

The softness in demand is just one problem, though. The other is a sizable increase in capacity, transforming a once-tight market into one glutted with available space.

Nowhere is this scenario more evident than in Los Angeles, the busiest U.S. gateway serving the Pacific.

In recent months, JAL, Nippon Cargo, Cathay Pacific Airways, Singapore Airlines and Malaysian Air have put freighters there, while Asiana Airlines, the new Korean carrier, has deployed a Boeing 747-400 combi, a plane that holds freight on the main deck as well as the bellyhold compartment. Singapore

plans to add a second weekly freighter flight between Los Angeles and its home base this summer.

The deluge of freight space, coupled with a large cadre of existing all- cargo and belly space, is making lives miserable for carriers serving the gateway.