Early on a December morning back in 1975, several area business leaders gathered for breakfast at the University Club.

They had been invited by Kenneth Sparks who heads the staff of the Federal City Council, an organization of major Washington executives that works primarily behind the scenes to promote the city.

David Barton, of Baltimore, was the speaker. And there was a bit of skepticism about his presentation that day, in which he suggested combining the entire Washington and Baltimore regions into a single package, for purposes of economic development promotion.

There were jokes about whether to call it Balwash or Washbal and questions about how Washingtonians could benefit from a promotion that included Baltimore. Didn't Washington have enough problems to solve? But the early doubters now have been convinced, and the United States is about to get a new and very rich marketing region.

A Baltimore/Washington Common Market is being created to promote the regional economy, complete with an intial annual budget of some $600,000 contributioned by Washington and Baltimore corporations as well as the state of Maryland.

According to Riggs National Bank Chairman Vincent Burke Jr., recently elected as initial chairman of a group representing businesses in both metropolitan areas, formation of a corporation to promote the D.C. and Baltimore region as a single package is necessary to exmphasize "the obvious that has to be stated. . .this area has a tremendous amount [of advantages] to sell."

The new regional promotion corporation will sell the local "common market" to businesses and institutions across the country and overseas, emphasizing a market approach favored by business over the jurisdictional promotion approach of the more aggressive area government development agencies.

Burke, who was among the small group attending the initial Washington presentation about a common market concept back in 1975, said the new effort "helps everybody . . . by bringing new tax dollars to the broad community." Once a business nstitution or organization becomes said on the greater Baltimore - Washington area, county can city governments can line up to promote a specific regional building site, he added.

Behind the drive of Burke and other executives such as Rouse Co. Chairman James Rouse, a key member of the Baltimore delegation, is concern over future employment growth in the region.

According to Barton, head of a Baltimore marketing and consulting firm, counties and cities in the Baltimore Washington region are expected to register a 50 percent population increase during the 1980s compared with 42 percent in Dallas-Port Worth, two highly touted growth markets.

In order to keep regional unemployment below 5 percent of the work force, however, about 75,000 new jobs per year must be created starting in 1980. Only a unified sales effort can assure this region the steady growth needed for jobs, in the face of competition for investment and corporate growth that has been accelerating in the past decade, the Washington and Baltimore leaders say.

By adding 1,000 new jobs in basic industry, the region would gain more than $1.48 million in new revenues per year, an additional 1,655 new jobs in retailing, services and other economic sectors and $22.6 million in new annual wages - all of which would filter throughout the area. A simple example of this process is leisure spending by Baltimore area residents coming to Capital Centre to watch the Washington Bullets and Washingtonians traveling to Memorial Stadium to watch the Baltimore Oriolets.

Here is what the new promotion corporation will sell:

The nation's fourth richest region in total spendable income at $30 billion a year, behind only greater New York, greater Los Angeles and greater Chicago, with a population of 5 million living in 18 counties or cities of Northern Virginia, Maryland and D.C. - stretching from Prince William and Charles counties to the south to Frederick, Carroll, Baltimore and Harford counties along the Maryland border with Pennsylvania.

A single economic trading area with the deep water port of Baltimore, the federal government in Washington and a growing base of industry and financial institutions in both centers providing the keys to sustained growth.

More research and development spending ($226 million in 1975) than in Massachusetts, often cited as the R&D center of America: more 60 colleges and universities and an above-average number of college-educated citizens: and the highest average family incomes in the nation (eight of the 50 richest U.S. counties are in the "common market").

Baltimore businesses have pledged $150,000 and Washington companies have pledged the same, while Maryland is to provide $300,000. Burke said the business leaders hope to win financial support from Virginia in the future and noted that he has received expressions of interest from the Norfolk and Richmond areas. An expression of the common market concept of Tidewater is not out of the question, he added.