A D.C. Superior Court judge struck down yesterday a city law that would have required the District's 147 largest real estate taxpayers to pay their annual tax bills in full this Monday.

The law, passed by the City Council in 1976 and approved by the mayor in 1977, required commercial real estate taxpayers with tax bills of $100,000 or more on a property to pay the full amount on Sept. 17 this year. Under Judge Paul F. McArdle's ruling, such taxpayers will now be able to pay their taxes in two equal installments -- normally due on Sept. 15 and March 31 -- as residential taxpayers and commercial taxpayers owing less than $100,000 have been able to.

John T. O'Neill, executive vice president of the Apartment and Office Building Association of Metropolitan Washington, said that the big taxpayers are "delighted" they will have to pay only half of an estimated $20 million in taxes they owed on Monday. The taxpayers affected by the decision are those that own properties worth at least slightly more than $5 million.

Colin Walters, assistant city administrator for financial management, said the deferral of $10 million in tax collections "is a blow" at a time when the city is trying to meet its payrolls and pay its debts before the end of the fiscal year Sept. 30.

"We were having a difficult time as it was," Walters said. "This will make it that much harder." But he added that there should be no effect on services the city provides its citizens.

The city owes the U.S. Treasury $40 million it borrowed to meet earlier obligations, expecting to repay it from this month's tax collections. Walters said the city may try to extend part of the loan.