The rapidly developing I-95 corridor between the Baltimore and Washington beltways is an economic gold mine with the benefit of a good road network that state officials said yesterday they hope to highlight in an aggressive campaign to attract more business to the area.

The 20-mile Baltimore-Washington corridor, state officials said yesterday, will be home to 87 percent of the state's 1.8 million-worker job force by 1990, representing a significant expansion in white-collar, service-oriented industry and a corresponding decline in the traditional employment sources previously based in such places as Baltimore's port and steel factories.

"We have to realize that Maryland is now a service sector state," said Hans F. Mayer, the deputy secretary of the state's Department of Economic and Community Development. "We're no longer a lot of smokestacks and blue-collar workers."

The biggest loser, Mayer said, will be Baltimore, which is projected to lose 25 percent of its manufacturing industry by then. But Mayer said that loss will be more than offset in the city and throughout the I-95 corridor by the high-technology, travel-related and research and development projects now springing up in Howard, Prince George's, Montgomery and Anne Arundel counties.

Mayer, state transportation secretary William K. Hellmann and others spoke to more than 100 members of the Laurel Area Chamber of Commerce who gathered at the Johns Hopkins Applied Physics Laboratory yesterday for the group's annual symposium on economic development.

They described the Baltimore-Washington corridor, bounded roughly on the east and west by Rtes. 3 and 301 and Rte. 29, as a "boom" area that is home to 80 percent of the 13,000 jobs created by new industry in Maryland since 1981.

The Laurel group also unveiled yesterday a $20,000 marketing film intended for use by recruiters and governments wanting to persuade out-of-state firms to relocate to the suburban area between the two cities.

"We are turning to a large extent into a megalopolis," said Robert Levan, an attorney who is chairman of the Laurel chamber. "It's just a continuation of what begins up in Boston and will probably extend to Richmond."

The idea of marketing the region as a corridor, some said, also will help to give a sense of identity to an area that has in the past lacked a sales strategy.

"Washington doesn't claim us," Laurel Mayor Robert DiPietro said. "Baltimore doesn't claim us. We're kind of like in no-man's land between the two cities."

The new Baltimore-Washington marketing cooperation is intended to include neither city, but is to focus exclusively on the area in between, a region that its boosters say is now coming into its own.

Exhibitors at the event showed off designs for existing and planned developments along the corridor that they said demonstrated their point about the vitality of the region. They included projects such as Konterra, an extensive 1,457-acre project that is expected to include office parks, residential areas and public facilities.