The Trump Shuttle made a bid yesterday to fill empty seats by offering advanced purchase discount fares during the workweek.

The discount fares go on sale immediately but will be in effect only until Sept. 2, during the normally slow summer season. The fares, which put the cost of the shuttle slightly below the cost of a round-trip Amtrak Metroliner fare between Washington and New York, are available during non-peak travel hours and are non-refundable.

Reservations must be made at least 14 days in advance, with tickets purchased no later than 24 hours after the reservations are confirmed. Total cost for the round-trip discounted ticket is $119 -- compared with the regular $284 round-trip fare.

"We think that gives the availability of the air shuttle market to those passengers who would not normally want to spend $142 each way," said Richard F. Cozzi, president of the Trump Shuttle.

The introduction of discounted fares comes at a time when shuttle traffic is in a slump, reflecting the continuing recession in the Northeast. Although passenger traffic has been improving every month this week, it was still about 15 percent below last year's level in April, according to the Pan Am Shuttle. Trump spokeswoman Joan Fudala said the Trump Shuttle is experiencing a similar weakness.

Both shuttles are currently for sale, with Northwest Airlines likely to take over operation of the Trump Shuttle. Cozzi said the deal may be wrapped up as early as the end of this week.

Although the Trump Shuttle lost $68.3 million in 1990, according to figures filed with the Department of Transportation, it has a positive cash flow, Cozzi said. Cozzi said it would break even if debt payments, which have been suspended while shuttle owner Donald Trump negotiates with his creditors, were resumed.

Several airlines, including Delta and United, have looked at various pieces of the remnants of the Pan Am empire, including its shuttle.

Essentially, the Trump Shuttle is adapting a marketing tool that has been used by other airlines for years to fill up flights that would otherwise carry a large number of expensive, empty seats. Because the discount fare is available during hours when business travel is light -- between 10 a.m. and 2 p.m. and from 8 p.m. until the last flight -- "they probably won't really be taking away any revenue from people who are already flying that route," said Raymond Neidl, an airline industry analyst with Dillon Read & Co. in New York.

"What they'll be doing is looking for tourists or backpackers who would have taken the car or hitched or taken the train," he said.

Pan Am spokeswoman Elizabeth Hlinko said the Pan Am Shuttle was studying the move but had not decided yet whether to match it. Last year, the Trump Shuttle instituted an advance purchase discount fare for weekend travel on the shuttle, which Pan Am did not match.

Cozzi said that the Trump Shuttle has taken several steps to control its costs, including reducing its weekend service. "We were generating 27 percent of our expense on weekends when we operated on an hourly basis and generating only 15 percent of our revenue," he said.

Eliminating nine flights on the weekends also freed aircraft and crews to fly charters, which have generated $15 million in the first four months of the year, he said.