The percentage of Americans two months or more behind in their mortgage payments increased slightly during the July-to-September period, but the percentage of borrowers who were 30 days or more late declined, according to a survey by the Mortgage Bankers Association of America.

The two-months-or-more delinquencies rose from 1.83 percent in the second quarter to 1.88 percent in the third quarter, while 30-day delinquencies dropped from 5.81 to 5.64 percent. The survey covered nine million mortgage loans totaling $306 billion in debt.

The three states with the lowest 60-days-or-more-delinquent rates are all in New England -- Maine, Massachusetts and New Hampshire. Virginia ranked fourth.

Warren Lasko, the association's executive vice president, said, "Delinquency rates should fall in the foreseeable future due to current lower interest rates, tighter loan underwriting and intensified loan servicing by lenders."

Columbia's developer, the Rouse Co., plans to seek a zoning change that would allow multifamily units in River Hill, the planned community's last undeveloped village, which currently is zoned for single-family detached housing.

A rezoning proposal calling for multifamily housing in Harpers Choice and Kings Contrivance also will be filed soon, said Alton J. Scavo, a Rouse Co. vice president.

The previous plan for River Hill called for 2,100 single-family detached houses on lot sizes ranging from one-fifth to one-half acre. The new plan would provide for 2,600 units, of which 1,100 would be duplexes, town houses or apartments.

The change would not affect Columbia's overall density of 2.2 units an acre because of an increase in open space that the zoning change would facilitate, Scavo said.

Under the change, River Hill would have the lowest density of any village in Columbia, with more than 50 percent of its 1,745 acres designated as open space, Scavo said. Ninety acres would be set aside for multifamily housing and 600 acres for single-family detached houses.

The Rouse Co. said it needs the rezoning because it wants more diverse housing in River Hill village, the 10th of Columbia's villages. River Hill is expected to be completed in the mid-1990s, Scavo said.

The Pennsylvania Avenue Development Corp. last month approved plans to renovate the old Evening Star Building at 11th Street and Pennsylvania Avenue NW, opposite the Old Post Office.

The 11-story marble structure, completed in 1898, was occupied by the Evening Star newspaper, later The Washington Star, until 1960. The renovation, which will include construction of additions to the west and to the north of the historic building, will provide 207,000 square feet of office space, 12,000 square feet of retail space and underground parking.

The project, being done by the Jonathan Woodner Co. of Washington, is expected to be completed by January 1989.

IN THE BUSINESS . . . Wade Investment Co., a Rockville real estate investment firm, has bought the Featherstone Square Shopping Center in Woodbridge for $9.27 million . . . Anthony Reynolds, a principal in the Washington appraisal firm of Reynolds & Reynolds Inc., has received the Appraisal Institute's Charles B. Shattuck Award given annually for an outstanding contribution to appraisal education . . . Stanley Martin Communities Inc. has bought the one-time W&J Sloane furniture store at 7220 Wisconsin Ave. in Bethesda for $2.75 million from Joseph O. Stuart and others . . . Chicago Title Insurance Co. is predicting that the Washington area will be the nation's fifth-largest residential construction market in 1986, with 37,800 housing starts. The firm predicts that Dallas-Fort Worth, with 64,600 starts, will be the nation's leading housing construction market, followed by Los Angeles, Phoenix and Atlanta . . . First Southern Mortgage Corp., formed this fall by Continental Federal Savings Bank and First Federal Savings and Loan Association of Northern Virginia, has opened its first two offices, at 7611 Little River Turnpike in Annandale and at 6500 Rock Spring Rd. in Bethesda. . . Construction has started on the 300,000-square-foot Clarendon Square office building at 3011 Wilson Blvd. in Arlington. It is being developed by the Phillips Development Corp. of Bethesda and built by Omni Construction Inc. . .. The Chesapeake Harbour residential community on Chesapeake Bay near Annapolis has opened a 200-boat marina . . . Prudential has opened the first of eight office buildings planned for the Willow Oaks Corporate Center at Rte. 50 and Gallows Road in Fairfax County . . . The National Association of Realtors reports that 91 percent of home sales this past fall were financed with a single mortgage, the highest recorded level of single-loan transactions in the three years the trade group has collected information on how Americans finance their home purchases. Only 5 percent of homes were financed with the help of a second loan, while 4 percent involved all-cash transactions . . . Construction has started on a 196-room Comfort Inn, part of the Quality International chain of hotels, at 500 H St. NW. It will be completed next summer . . . The 200-room Washington Dulles International Hotel has opened on Rte. 28 in western Fairfax, opposite the airport. It is part of the new Renaissance Centre, a $44 million complex that includes the adjacent 300,000-square-foot Hallmark Building . . . KB Theatres has broken ground for a five-screen movie theater at the Calvert Village Shopping Center in Prince Frederick, which will be Calvert County's first movie theater since the mid-1950s.

THE PERSONNEL FILE . . . Omni Construction has promoted James A. (Bo) Hooff, Barry D. DePauw and Snead W. Luck to vice presidencies . . . Comprehensive Marketing Services Inc., an international real-estate-related consulting firm, has named Debbi Hurd as vice president of the newly created development department. Jerry Doctrow has joined the firm as vice president for loan servicing . . . C. John Ruppert and Edwin A. Bentley are new vice presidents at Norwest Mortgage Inc. in Rockville . . . Realty World Corp. has promoted Jerry Burgess to vice president . . . KMS Group Inc. of Columbia has named Wilbur E. (Pete) Simmons Jr. chairman, Peter Kirk president and chief executive officer and J. Richard O'Connell general counsel. At the same time, the company has affiliated with Broventure Co. of Baltimore as an equity partner.