Robert V. Brown, a teacher who has worked as a candidates' advance man in two national political campaigns, has announced his candidacy for the Democratic nomination for an at-large seat on the D.C. City Council.

A lifelong Washingtonian, Brown was the fifth entrant in the Sept. 12 primary race for the one citywide seat that is available to a Democrat. The incumbent, Marion Barry, is running for mayor. The city charter reserves the other seat that is to be filled this year for a member of a minority party.

Brown made his announcement Saturday to a group of supports in the Sylvan Theater on the Washington Monument grounds.

He said he would stress housing and economic development and urged that the real estate tax be reduced from the present level, which he called "ridiculous."

"I want to see a united Washington," Brown told a reporter. "I want to see the business sector united with the white and the black and the Hispanic. I am an idealist."

Brown, who is single and in his 30s, attended Howard University and was graduated from D.C. Teachers College. He has taught for eight years and currently is assigned to the adult education program.

He is a member of the D.C. League of Women Voters (which is now open to male members) and said he served as an advance man in the presidential nomination campaigns of the late Sen. Robert F. Kennedy (D-N.Y.) in 1968 and the late Sen. Hubert H. Humphrey (D-Minn.) in 1972.

His campaign headquarters is at 111 Kennedy St. NW.