Washington builder-developer Michael G. Cappy plans a multi-million-dollar Dulles World Trade Center with a 372-room hotel and acres of permanent exhibit space.

The developer said last week that he has acquired a 60-acre site at the southeast intersection of the Dulles airport road and Rte. 657, two miles east of the airport. He said the first phase, to start this spring, will include a 145,000-square-foot trade center and exhibition hall and a "full-scale luzury hotel."

Cappy said the total development project's first phase should be completed in 1980, and one million square feet of office and exhibit area will be ready in five years.

Architectural plans for the $23 million first phase of construction have been prepared by Charles W. Englehart of Annapolis. Cappy said the trade center would enable both American and foreign manufacturers to display their products and have offices under one roof near an international airport.

"There are similar flourishing trade centers in major foreign cities and in New York, Boston, Dallas, Houston, San Francisco and Los Angeles," added Cappy. "I am convinced that we can attract manufacturers of products from cameras to hardware items."

David Edwards, executive director of the Fairfax County Economic Development Authority, said the project sounds promising and added that the entire Dulles area appears primed for more international-trade-related development. He cited Virginia plans for construction of toll lanes for access traffic along the present Dulles nonaccess highway as contributing to recently increased interest in new development from Reston to the airport.

Land transactions and prices have been increasing in the Dulles area in recent months, according to broker William Bryant, a specialist in that area. Bryant said land prices for sites with frontage on the Dulles road have tripled in the past year to $45,000 an acre for large undeveloped tracts with sewer and water services available.

Expressing confidence in the project by Cappy, Bryant added that garden industries, corporate headquarters, hotels, convention centers and trade associations are among the areas of current interest for development of those locations.

Bryant said an Iranian investment group recently bought 833 acres on Sully Road, near Dulles but in Loudoun County, for $5.5 million and that a Swiss group bought a site with frontage on the Dulles road. Last fall, Sperry Rand Corp. bought 35 acres in Reston for a research facility and paid "$1.50 a square foot," according to Bryant.

A large chunk of available development land in the Reston-Dulles area was sold last year to Mobil Corp.