Royce Hanson, the urban specialist and unsuccessfull office seeker who has headed Montgomery County's influential Planning Board for the last decade, has announced he will resign his post effective Feb. 20.

"I have reached an age where it is imperative that I either return to my profession or leave it permanently," Hanson, 49, said in a letter submitted to the County Council. He has accepted an offer from the National Academy of Sciences to direct a four-year study of urban policy.

Hanson was appointed Planning Board chairman in 1971, as the rapid growth that began in Montgomery in the 1960s was causing problems of suburban sprawl and school over-crowding and gobbling up the county's open land.

He emerged as a strong and often controversial advocate of a firm government hand leading the way to phased, orderly growth. "I do have ideas," the former university professor once said. "If after devoting 25 years of my life to government, I had no ideas, I wouldn't be worth the powder to blow me up."

Hanson received fire from all sides. Citizen's groups complained he was putting too much new housing in their communities, while developers saw him as favoring too many controls on construction.

Three times during his term as planning chairman, Hanson unsuccessfully sought elected office. He ran twice for Congress in the 1960s, and in 1978 lost the Democratic nomination for county executive to Charles Gilchrist. Many people in county government had assumed his ambition would eventually lead him to resign his current post.