Business leaders from Washington and Baltimore spent most of the past two days engaging in some old-fashioned boosterism.

It's their hope that the tale of two cities' rapidly increasing development as hubs of a major common market will be repeated often enough to attract U.S. and foreign investors in greater numbers.

Thus, business executives and economic development experts from both cities played host to national media representatives in two days of briefings and tours under the aegis of the Washington-Baltimore Regional Association.

"It's boosterism, but well-deserved boosterism," observed Gail Garfield Schwartz, a Washington-based economic consultant who participated in Monday's briefing in Baltimore.

At a similar briefing here yesterday, J. Pat Galloway, president of the Greater Washington Board of Trade, unabashedly declared: "We don't try to hide it. We're selling" the area. "It's a great place to do business."

The story is a familiar one to residents of the Washington-Baltimore region. It's the fourth most populous metropolitan market. Median household income of more than $23,000 is the highest in the United States. Effective buying income is ranked fourth-highest, but is rising faster than anywhere else and is projected at $65 billion by 1983.

At one end of the Washington-Baltimore corridor lies the nation's capital, developing rapidly as a financial center, enjoying a commercial building boom, increasing in importance as a location for corporate headquarters and traditionally recession-resistant.

At the other end is Baltimore, Maryland's financial and industrial center and the nation's second-largest container port--one that serves all of the major manufacturing centers of the United States.

Although business leaders in recent years have developed fairly strong campaigns to sell the region as a common, robust market, their efforts have been fragmented.

For the most part, marketing programs developed by the Greater Washington Board of Trade have focused on the Washington Standard Metropolitan Statistical Area. The board's counterpart, the Greater Baltimore Committee, and that city's economic development corporation understandably have been concerned with business and economic development there.

However, a group of business executives from the two cities concluded five years ago that the metropolitan areas and the corridor linking them constitute a major common market with unlimited potential. The WBRA, the vehicle they chose to promote that idea, has floundered until recently.

The concept of the WBRA as an umbrella organization to coordinate common market activities remains viable, several business executives from Washington and Baltimore insisted this week. "We tried to move too fast," said Jerome W. Geckle, president and chief executive officer of PHH Group Inc. in Hunt Valley.

"You have to crawl before you walk. We're now back to the crawling stage," Geckle said.

Meanwhile, although commercial and business development in and around each of the cities has followed sharply different patterns, it has attracted considerable interest from potential investors.

Baltimore is experiencing a renaissance after years in which its commercial areas downtown had deteriorated and were all but written off. The highly publicized Harborplace and nearby Charles Center symbolize a rebirth of the city.

More than that, they're examples of a "public-private partnership--successful but unstructured," explained Walter Sondheim, chairman of Charles Center and Inner Harbor.

Economist Robert R. Nathan believes competition between Washington and Baltimore, as well as a common interest they share, will benefit both cities in the long run.

"They will reinforce each other" because of their "complementarity," Nathan said.

On the other hand, serious problems will emerge as the areas grow toward each other, he said. Environmental issues, competition for water, and adequacy of sewer treatment facilities will become major problems for government and business leaders of the two areas in years to come, Nathan believes.

Nonetheless, "Further cooperation will evolve," he said. Meanwhile, "it will be interesting to watch this area" as the government sector contracts.

In the next year or so, regional ties and growth in the high-technology industry will tend to cushion the area--normally recession-resistant--from the effects of a sharp reduction in the government sector.

"I think this region will benefit from lower interest rates and an improved economy with new capital formation," Nathan said. "This region will be one of the healthiest and most expansive in the country as a result of the emphasis on research and development."