The Washington-Baltimore Common Market, already one of the fastest-growing areas in the country, is expected to gain at least 360,000 jobs by 1990, according to projections contained in an economic profile released today by one of the region's leading business organizations.

Nearly a third of the projected increase in employment is likely to be in the rapidly growing service industries, according to the Washington-Baltimore Regional Association, a nonprofit alliance of business leaders from the Washington and Baltimore areas.

The expected surge in job increases is part of a pattern of economic growth the region has experienced during the past five years and one that is expected to continue "unabated in the immediate future," the WBRA noted in its third edition of "An Economic Profile."

Although the organization boasts of continuing economic strength in the common market, it cautions that national events will play a major role in determining how rapidly employment actually will grow.

In the meantime, the WBRA is projecting a 50 percent increase in total government purchases, almost a doubling in personal income and a rise of 77 percent in median household income by 1990.

Figures compiled by the WBRA show that the common market currently ranks fifth in total retail sales ($31.9 billion), sixth in value of commercial construction ($682.3 million), and is the second-largest office market in the country, behind New York, according to WBRA. The figures are based on 1983 year-end totals.

The economic profile shows further that consumer expenditures totaled $58 billion in 1982, when personal income was an estimated $76 billion and the median household effective buying income totaled $30,200 -- the highest in the nation.

For the first time since the WBRA began publishing the economic profile in 1980, the publication assesses the impact of the federal government on the BW common market. Federal contract awards made in the Baltimore-Washington region in 1983 totaled nearly $9.5 billion, or 6 percent of the total federal expenditure of $158.9 billion, the WBRA publication avows. WBRA also estimates that by 1990 government purchases will increase by 50 percent.

The common market, as defined by the WBRA, includes the metropolitan statistical areas of Baltimore and Washington, and St. Mary's County in southern Maryland. One of the strongest housing markets in the country, the area has a population of 5.6 million and is expected to gain more than 700,000 residents by 1990.