Jim Backas, head of the District's Commission on the Arts and Humanities, has resigned after 18 months in the post to become head of the Maryland State Arts Council, the mayor's office said.

Backas, 57, who served as the mayor's adviser on cultural affairs, said that on May 1 he will move to the position in Maryland that he held in the early 1970s.

When he came to the D.C. commmission in 1984, the agency's budget was about $1.1 million. According to Barry, it will exceed $3 million in fiscal 1987. "We built a lot of programs and the budget is up," said Backas. "Now it's time to go and do it for Maryland."

Barry said that in the past seven years the commission "has become a strong and stable influence in the arts community" and that it "is building a national reputation." He noted that the commission has developed programs to serve the elderly, the handicapped and the institutionalized, and that a summer program provides summer jobs to artistically gifted youths.

Backas said was "quite proud" of the Comprehensive Arts Development Program he developed to strengthen small and midsize arts groups and to take art to areas of the city where there had been little cultural activity. The program encourages churches, schools and community groups to present concerts, art exhibits and other cultural events in their neighborhoods.

Barry said the commission will initiate a mural program and a festival program this summer and will soon begin a $1.7 million program to establish a cpaital improvement fund to pay for construction and renovation of facilities related to art activities.

Backas, who served as special assistant to the chairman of the National Endowment for the Arts and headed a national lobbying organization for the arts, said he decided to return to the Maryland agency because "they made me a good offer . . . and it seemed like a pleasant and challenging thing to do."