More than 15 condominium projects in the District will go on the auction block next month unless their owners pay the city government overdue property taxes totaling more than $250,000.

City officials and some developers say that the unusually high number of condominiums on this year's list of properties facing tax auction is a reflection of the sharp downturn in the once-strong condo market here.

The luxury and moderately priced developments, located from Connecticut Avenue to Anacostia, are among some 4,000 properties facing tax sale Jan. 18.

This year's list is about half as large as last year's, but the number of condo projects on it has more than doubled, according to an official in the city's Department of Finance and Revenue, who said that fewer than six such developments appeared last year.

The list "does seem to include a lot more condominiums," said Jeffrey L. Humber, acting director of the department. He attributed the increase to the steep decline in condominium sales, which are down 50 percent from last year.

"Some of the developers are in pretty tight cash situations," he said.

Developer David Clark (not related to D.C. City Council chairman-elect David Clarke) agreed. Clark owes nearly $70,000 in taxes for units at three projects, including the Iowa and Mondrian near Logan Circle.

"The condominium market was so slow we could not market them at the pace we planned and this created a shortgage of cash," said Clark. He said he is selling unsold units at these two projects and at Envoy Towers on 16th Street to investors, and will pay the taxes next week.

G.V. (Mike) Brenneman, president of the Washington Board of Realtors , said some builders with slow sales find it cheaper to owe the city than borrow the needed money.

The city charges a flat 10 percent penalty for overdue taxes, plus a12 percent-a-year interest penalty, which is lower than the rates charged by many banks on short-term loans, Brenneman said.

If their property were sold in a tax auction like the one scheduled for January, city law gives the developers two years to pay off back taxes and reclaim the land before the title actually passes to the high bidder in the tax sale.

Some developers whose condominiums appeared on the list published last weekend said their failure to pay taxes was simply a mistake.

Steve Z. Laufer, an economist who is the major owner of the Northbrook condominiums at 3426 16th St. NW., said he failed to pay an estimated $30,000 in taxes through "an oversight," and added: "It will be paid promptly. There is not the remotest possibility of that property going up for sale."

Other condominium projects that owe the city more than $10,000 in delinquent taxes include 2138 California St. NW, 2301 Connecticut Ave. NW, The Concord at 1815 New Hampshire Avenue NW, and a group of town house condominiums on Oregon Drive NW. The owners could be reached for comment.

Two of the delinquent properties on the list are city-sponsored condominium projects located at 1421 Columbia Rd., NW and 1420 Harvard St. NW.

The city sold the apartment buildings to a group of developers who were to renovate and sell them. But sales were sluggish and the city stepped in and agreed to subsidize the mortgages so low and moderate income families could afford to buy.

One of the owners, developer Frank Calcara, said $6,000 in taxes was unpaid because of delays in closing sales of units. Humber said he was "a little surprised" that the list of properties facing auction had shrunk this year, "considering the economic climate."

He attributed the reduction from last year's 7,750 properties to a new format for city tax bills, which show unpaid taxes as well as the current bill, and to increased efforts to make certain that bills are sent to building owners' correct addresses.