JESSUP, Md. (AP) _ From the humble acorn comes the mighty oak, and from a tiny motel in a sleepy Maryland town, sprang the largest truck stop on the East Coast, soon to be matched by the largest privately operated bus stop in the nation.

The blue and white standard issue highway sign on Interstate 95 gives no clue to the size of the Truckers Inn - its seven retail stores, showers, pool, service station, 24-hour restaurant, bar with live music, 140-room hotel and a parking lot large enough to accommodate 25 football fields.

''On one-to-10, this is a one,'' said Larry Holt, a truck driver for 15 years.

Most truckers only stay at Truckers Inn overnight, many sleeping in the cabs of their trucks, stopping in to see a truck broker, use the telephones or showers, or sample the famed strawberry pie. Some, however, spend several days there waiting for their next load.

The Truckers Inn was started in 1978 by Garth V. Davis, who was chief criminal investigator for the Howard County Police.

Davis said he had never even looked at a truck before then. His involvement in the business began with the investigation of a December 1975 murder of a motel manager in nearby Elkridge.

In addition to solving the crime, Davis solved another problem: How to bring his mother and father, recently retired from the Air Force in Oklahoma City, closer to where he and his sister, also a Howard County police officer, live.

He suggested that his parents manage the Jessup motel.

At first business didn't do so well, Davis said.

''I started arranging for taxis to pick (truck) drivers up at service station'' a few miles from the motel, he said. The rest, as the saying goes, is history, with the Truckers Inn growing into a $15 million-a-year business.

Now Davis is focusing on getting his Baltimore Travel Plaza started in east Baltimore. He envisions it as ''The Place on the East Coast for buses traveling on the north-south route.''

Walking over to an artist's rendering of the project, to be completed in November, Davis observes with pleasure how his new business is nestled by the interstate ramp, the pathway for 100,000 vehicles.

''I like putting the puzzle together,'' Davis, 44, said of the many pieces required in the $36.5 million dollar plaza, which features truck and bus service areas, restaurants, a movie theater and a 180-room Quality Inn.

He compares the complexity of the project with a criminal investigation - work, he says, he still misses.

Ron Ziegler, the former Nixon White House press secretary who is now president of the National Association of Truckstop Operators, said Davis' projects are typical of third generation truck stops.

Ziegler said the truck stop - no more than a roadside cafe in the 1950s - expanded services in the 1960s with the development of the interstate system.

Today, Ziegler said, truck stops are ''among the largest feeders of the United States ... behind McDonald's and Wendy's, and so forth.''

Although now a successful entrepreneur, Davis continues to maintain close ties with law enforcement officials, participating in efforts to crack down on drug use among drivers and solving other crimes as well.

Using the truckers radio network and his own investigative skills, Davis said, he helped North Carolina and Maryland state police find the killer of a hitchhiker from Odenton, Md.

Work performed by his special security force also led to the arrest of a trucker who was selling stolen frozen turkeys on the Truckers Inn parking lot.

End Adv Weekend Editions June 21-22