The Reagan administration's plan to impose user fees, or taxes, on government-sponsored mortgage agencies would increase the federal deficit, not reduce it, according to a new study by an economic forecasting firm.

Lawrence Chimerine, chairman and chief economist of Chase Econometrics Inc., said that "in each of the economic scenarios used to analyze the impact on the economy of the fees . . . we found that their successful imposition would raise mortgage rates, reduce housing starts and sales, reduce jobs and increase the deficit."

The administration is proposing that various transactions of the Federal Housing Administration; the Veterans Administration; the Federal Home Loan Mortgage Corp., known as Freddie Mac; the Federal National Mortgage Association (Fannie Mae); the Government National Mortgage Association (Ginnie Mae); the Student Loan Marketing Association (Sallie Mae) and the farm credit system be taxed.

Fannie Mae, which purchases mortgages from savings institutions and mortgage bankers and then resells them on the secondary market, commissioned the Chase Econometrics study to try to assess the effect of the user taxes on it.

Chase said, among other things, that with declining interest rates, if Fannie Mae can pass on the user taxes to homeowners, there would be 163,000 fewer housing starts in the 1988-92 period, 320,000 fewer housing sales and lost output of $24 billion, resulting in a greater federal deficit.

If interest rates are increasing, and Fannie Mae is unable to pass on the user tax, Chase said Fannie Mae would lose $300 million by 1989 and have to halt its purchase of mortgages. Housing starts would be cut by 75,000 in 1989 alone and home sales by 100,000. Again, Chase said the federal deficit would be increased, not reduced by the fees.

The administration made a similar user fee proposal last year, but it was deleted from the budget when the housing industry successfully rallied pro-housing advocates in Congress.

Fannie Mae is offering 22 homes for sale that it has acquired through foreclosures in the District, Brandywine, Bowie, Germantown, Landover, Lusby, New Carrollton, Pasadena and Seat Pleasant.

The properties, ranging in price from $19,900 to $117,900, are described as "relatively new and in good condition," according to Fannie Mae's president, Mark J. Riedy. "Many are highly suitable for low- and middle-income families and also are available to investors."

Buyers who plan to live in the homes can put down as little as 5 percent, while investors will be required to make 20 percent down payments. Maryland residents can get more information by calling 1-800-221-4636; residents elsewhere can call 1-800-553-4636.

Northern Virginia home sales increased by 35 percent last month over January 1985, up from 1,327 to 1,790, according to figures compiled by the Northern Virginia Board of Realtors.

"This year there has been no winter slump in real estate sales," said board President William Laughlin. "Undoubtedly, buyers and sellers are taking advantage of the low mortgage interest rates."

Of the 1,790 units sold, 203 of them were condominiums costing an average of $74,970. The remaining 1,587 town houses and detached homes cost an average of $134,100.

Citizen task forces in each of Fairfax County's eight magisterial districts are debating the merits of numerous proposed changes to the county's comprehensive land use plan.

The changes, initiated by landowners, developers, members of the county planning staff or planning commission, total more than 150 countywide.

Task forces will make recommendations on proposals affecting the area they represent to the county planning commission. The commission, in turn, says it will consider those recommendations and advice from county planners before deciding whether individual proposals merit consideration and a public hearing, according to county planning official William Keith.

The Centreville task force will meet Monday and Tuesday at 7:30 p.m. at the government center in Reston. The Mount Vernon group will meet today at 9:30 a.m. at the Mount Vernon Government Center. The Lee District Task Force will meet March 4 at 7:30 p.m. at the Mark Twain School.

Two meetings are scheduled by the Mason District Task Force, today at 9:30 a.m. and March 4 at 7:30 p.m. at the Mason Government Center.

The Providence District Group will meet Thursday at 7:30 p.m. at Oakton High School. The Annandale session has not been scheduled. Meetings in Dranesville and Springfield were held late this week.

IN THE BUSINESS . . . Developer Coakley and Williams Inc. is planning to start construction next summer on the third phase of the Maryland Trade Center, a $24 million, 230,000-square-foot office building that will adjoin two other buildings and a Holiday Inn . . . Long & Foster is sponsoring three free home sellers seminars, in Camp Springs next Wednesday, in Annapolis on March 3 and in Rockville on March 10 For reservations, call 939-8511 . . . The National Association of Realtors plans to help the Federal Housing Administration and Veterans Administration sell their repossessed properties in seven metropolitan areas throughout the nation this year, including the Washington area. The plan involves distribution of FHA and VA property listings to licensed real estate agents who want them, particularly through regular computerized lists of available properties . . . Great Western Savings has made the single largest loan in the company's 99-year history -- $120 million in permanent financing for the Bethesda Metro Center, built by developers Alan I. Kay and Allen E. Rozansky . . . The Maryland Improvement Contractors Association has named three remodelers as contractors of the year, Welsh Construction Remodeling Co., Streuver Bros. Eccles & Rouse and Fireside Home Remodeling . . . Prudential Insurance Co.'s "mortgage by phone" program is now operating in all 50 states, with fixed- and adjustable-rate mortgages available in any amount, contingent on individual qualifications and situations . . . Oxford has completed its first "signature office building" -- the Oxford Building in Greenbelt, near the intersection of Kenilworth Avenue and Greenbelt Road . . . Evans Co., a commercial real estate development firm, has bought Park Place at Tysons, an 11-story office building in the Westpark area of Tysons Corner. The 260,000-square-foot building is currently leased to 26 tenants.

PERSONNEL FILE . . . Financial Service Group Inc. at Tysons Corner has named John R. Potvin as president of its property management division, Financial Service Equities Inc. . . . Richard C. Nelson, regional vice president and managing director of the Hyatt Regency Washington on Capitol Hill, has been re-elected president of the Hotel Association of Washington.