Nathan Landow, the Bethesda developer who plans an autumn start of an office building on a 28,000-square-foot site at 12th and F NW in the Metro Center area, has been named Maryland chairman of fund raising for the Carter-Mondale re-election committee. . . The Hawthorne Hotel, 2134 G St. NW in George Washington U. campus area, was sold recently for $600,000 to MWP Limited Partnership . . . Recently opened for Section 8 rent subsidy housing at 15th and Fern streets in S. Arlington, the handsome Claridge House has 300 apartments for mature persons. The development group was headed by Morrie Lipnick, a veteran builder. . . Forty-nine town houses priced over $120,000 are being planned by builder Herman Porten (formerly Page Construction and now U.S. Home here) on a bypassed site near Strathmore Lane and Rockville Pike near the Metro station across from Georgetown Prep and Gerard LaVay's completed Crest at Wickford town houses.

Open several months on Georgia Avenue in the Montgomery Hills section, the realtor office of Ernie Banks, 32, is primarily black staffed.But Jean Green, who describes herself as a white person over 60, has been hired as the new office secretary. She said boss Banks is not to be confused with the former famous Chicago Cub baseballer of the same name. . . .Conrad (Pat) Harness, the real estate editor on this newspaper about 30 years ago, has been a builder in Houston for nearly 20 years. He recently was among those selected for the "hall of fame" established two years ago by the National Association of Home Builders.

Henry Long, the principal who is amicably leaving Long & Foster Real Estate after an 11-year partnership with Wesley Foster, said he plans to concentrate on construction and development with builder Bruce Scott. They are already active in Manassas. . . Mallory Walker, head of the Walker Dunlop mortgage banking and realty firm, was surpised on his recent 40th birthday by finding his office filled with black balloons. He survived the day.

Due to an editing mix-up, it was stated incorrectly last week in this space that the Golubin & Warwick realtor firm is moving to another location. In fact, the firm is staying put in Old Town Alexandria but opening new offices in both the Del Ray-Potomac Yards section of Alexandria and in Potomac. . . Lois Gibson of Protocol/Washington says that new firm is one of those, including Courtesy Associates and Executive Offices, that supply furnished office space for persons wanting small, furnished offices with full services. One full floor of the 1100 17th Street building is used for that purpose. Average price per month to tenants ranges from $575 to $1000.

Lansing Valk, 86, a retired appraiser and real estate salesman, was the recent guest of several realty friends at a birthday lunch in midtown. They said Valk is still active and enjoying a healthy life with his wife of many years at their long-time residence on New Mexico Avenue NW.