The cab business was slow at National Airport yesterday.Some drivers waited in the 96-degree heat for more than two hours for a passenger.

Meanwhile, riding toward the District on a 50-cent subway Farecard was Allan Hodges, returning from a plane trip to Chicago. "Metro's quieter, it's air-conditioned, and I don't have to listen to loud rock music or (the driver) bitching about something," he said.

Hodges said he even selected United Airlines rather than the one he usually flies because its terminal is closer to the Metro station.

Thomas B. Parker, a cab driver for 15 years, said Metro "is definitely going to kill the cab drivers."

passengers used to ask for tours of Washington, Parker said, but then "the tourmobile killed that business." Now it's taking the airport trade, he said.

The opening of Metro's subway Blue Line linking National Airport to the Robert F. Kennedy stadium and points in between only a week ago already has had an impact on the airport cabbies. Some of them it is only the time of year - business always is slow in July and August - and others say it is too early to tell.

But Parker says, "Everytime you see a person on that Metro, that's a fare we don't have."

"That's too bad," Metro rider David Daufman said. "Cab drivers can all get jobs on Metro if more people ride it."

Kaufman said he saves about $5 each way by taking the subway and a metro station is close to his job.

About one-third of the passengers on one Metro car heading for the airport about 3 p.m. yesterday had at least one piece of luggage and were going out of town. All of them said they would save between $4 and $5 by taking the subway, and it was more convenient, quieter and cooler than taxicabs.

"Most of the time I get a cab, it's not even aire conditioned," said Carter Hoyle, a suburban Maryland resident walking briskly to catch a train. "At this time of day cabs get stuck in traffic. I don't have to worry about that."

"It's faster and plus my car's parked at work," said Doris Lumpkins. She said the congressman she works for, Rep. Don Edwards (D-Calif.), also takes the train to the airport on trips.

Cab dispatchers at the airport, however, were unimpressed with the amount of business Metro had syphoned off from cabs. "I really can't see where they've (Metro) done that much business around here," said dispatcher Don Neher. He said the subway relieves cab drivers of short uneconomial trips to Rosslyn or Crystal City.

"It's going to be all right," said Monroe Reeves, a cab driver for 26 years. "It's just a novelty. I'm going to ride it myself as soon as I can get some time."

Business travelers with expense accounts and people with several pieces of luggage will still be faithful cab riders, according to cab driver Ann Gilsenan. She said passengers take Metro to the airport because it's faster, but they ride back from the airport in the cabs because the Metro stops usually are not close to their homes.

"We're just waiting for a change," Parker said, fanning the overheating engine of his cab with a rag. "It may be a novelty. When winter comes I don't think they'll be wanting to walk that far," he said, pointing to the Metro station 1,225 feet away across a two-block long line of cabs waiting for their fares.