Federal Express Corp., the fast-growing overnight small-package airline, has no immediate plans to enter the passenger airline business, Frederick W. Smith, its chairman and chief executive officer, said yesterday.

In response to a question following a speech to Areo Club, Smith said the airline had looked long and hard at the possibility of providing passenger service -- it already holds some authority from the Civil Aeronautics Board -- but it came to "the horrible realization" that those already in business were doing a pretty good job. "We don't see the same opportunity we had in the cargo area," he said.

There Smith saw " a gap in the market" seven years ago and started an air-express service that guarantees overnight delivery. There existed a "tremendous bottleneck in transportation" that denied many businesses outside the major centers in the United States quick delivery of parts they didn't want to keep in inventory in installations all over the country, Smith said.

Since its first day of service on April 17, 1973, when its 10 planes carried 18 packages, Federal Express has grown into a booming business whose revenues in the year ending May 31 were $425 million. now the company carries more than 65,000 packages daily using 8,000 employes and a fleet of more than 50 planes -- 20 Boeing 727s and 737s and 32 Falcon Fanjets -- and 2,000 radio-equipped vans.

"Our hands are full" in the cargo area, he said, although he noted there "may be a niche for us in the charter business."