The president of the Washington-Baltimore Regional Association has resigned to accept a position with a local public relations firm, amid increasing uncertainty within the organization about its role in promoting economic growth of the region.

Barry Zorthian, who had been president of the organization for the past two years, said yesterday he isn't certain when his resignation will become effective.

However, Zorthian said he expects to leave WBRA soon to join the public relations firm of Gray & Co.

Zorthian said he had originally committed himself to two years with WBRA when he was appointed president in 1979. With more than two years in the job, Zorthian "feels that it is time to return to his original plans for his personal future," WBRA chairman Vincent C. Burke Jr. said in a brief statement released yesterday by the organization.

Burke commended Zorthian for his work with WBRA and said there will be no steps taken to select a successor until the association's executive committee completes discussions of next year's program and the organization's future.

Burke could not be reached for further comment on Zorthian's resignation or the nature of those discussions.

In a letter to Burke, Zorthian described WBRA as a "going organization." He added that the concept of regional economic cohesion is well-established.

Although the concept has been embraced by business leaders here and in Baltimore, some members of the association's board of directors privately expressed concern over its progress to date.

The key issue, said one director, is deciding what role the WBRA should play in promoting and attracting economic development for the region without duplicating the efforts of similar organizations and government agencies.

While several organizations have formulated economic development programs geared to their respective jurisdictions, WBRA has sought to promote the Washington-Baltimore region as a single market.