Royce Hanson, the chairman of the Montgomery County Planning Board and a well-known figure in county politics for more than a decade, yesterday formally announced his candidacy to succeed retiring County Executive James P. Gleason.

Hanson joins a field of candidates that is expected to grow before the Sept. 12 primary election. Montgomery County Council member John Menke, State Senator Charles W. Gilchrist and economics consultant Scott Fosler already have entered the Democratic primary. Albert Ceccone, a Bethesda realtor and Richmond M. (Max) Keeney, an official of the Air Force Association, which publishes an aerospace industry magazine, are the Republican candidates.

The Democratic party in Montgomery has a history of contentious primary races that often throw county-wide offices to Republicans despite the county's overwhelmingly Democratic registration.

The county executive's post has been occupied by Gleason since its inception eight years ago. Gleason withdrew from the race - although he was considered an easy victor - because he said he was frustrated as an administrator and wanted to write instead.

Hanson, 46, a Democrat, announced yesterday on the steps of the County Office Building, surrounded by supporters including former Montgomery County Council chairman Norman Christeller, former Court of Specials Appeals Judge Alfred L. Scanlan, and Vera Berkman, board chairman of the Washington Suburban Sanitary Commission.

Hanson, an urban planner by profession, said he will stress the need for more roads in the county to facilitate orderly economic growth, as well as an increased supply of housing in the county. He said that ideally the county executive race will require $100,000.

Hanson is one of the most formidable entries in the race to succeed Gleason, a Republican and the only county executive the county has ever had. In 1970 the county's form of government was changed from that in which the County Council appointed a county manager, to the current one, in which the executive is elected independently of the seven-member council. Hanson served on the charter commission that designed the change.

The Montgomery County executive manages a budget of $568 million, and is responsible for more than 5,000 employes in 30 different departments. By virtue of his ability to introduce his own legislation, and veto council proposals, the county executive in theory can be one of the most powerful elected officials in the Washington metropolitan area.

One veteran Democratic Party observer said that Hanson immediately becomes an imprtant factor in the race for the county executive post because he "is the only candidate who excites opposition. He has the antidevelopment people against him."

Hanson has in the past encouraged construction and economic growth in the county that has aroused the ire of the county's strong antigrowth forces. In Montgomery County's often faction-ridden Democratic party, opposition to a strong candidate often has allowed lesser known candidates to win primary elections.

Democratic observers in the county believe that while Menke, Hanson and Gilchrist are better known in the county than Fosler, Fosler has strength among liberals - a strong element in county politics.

"If Hanson appears to be gaining strength, people will desert Fosler to support Gilchrist," one politician speculated.

Menke, 37, County Council member for the past four years, left his job in 1974 as a physicist to successfully run for office after leading community protests over sewage treatment problems in the county. His campaign will be based on "what I've done in the last five years of council and civic work." He was a leading opponent of the proposed Dickerson sewage treatment plant, which had been unsuccessfully advocated by Gleason.

Gilchrist, 41, has been active in party work for the past 12 years, and state senator from Rockville for the past four years. An attorney with the Washington firm of Lee, Toomey, and Kent, he said, "my expertise in state affairs is sadly lacking in the county government."