The Supreme Court decision requiring the Census Bureau to do a traditional head count next year will raise the cost of Census 2000 by $1.7 billion, the Commerce Department said yesterday.

That is in addition to the $2.9 billion already requested for fiscal 2000 for the count.

"This is evidence that in the absence of using modern statistical methods, it is simply going to cost a lot more to do the census," Census Director Kenneth Prewitt said in an interview.

House Appropriations Committee spokeswoman Elizabeth Morra took issue with the bureau. "The 2000 census continues to be plagued by operational difficulties and cost overruns and these are problems that are unrelated to the Supreme Court's decision," she said.

But Rep. Carolyn B. Maloney (D-N.Y.) of the House Government Reform Committee's census panel said, "Today the bill came due for the Republican Census lawsuit."

Prewitt said the bureau will have to increase its advertising and other efforts to get people to respond to mailed questionnaires, will visit more homes that do not mail forms back and will need to hire more people and keep local offices open longer.

"If a significant number of persons don't mail back their questionnaires, the Census Bureau must redouble its efforts to reach every single person in every household--a task that is expensive because it is so labor-intensive," he said.

Americans sent back 66 percent of Census forms in 1990, and the bureau is anticipating that the return rate could fall to 61 percent this time. Each one-point drop costs an additional $25 million in follow-up efforts, Prewitt said.

Original cost estimates for the once-a-decade effort to count Americans were thrown into confusion in January when the Supreme Court ruled that statistical sampling could not be used to produce the numbers for use in congressional reapportionment.

The Census Bureau had planned to use sampling in the overall count, contending it would save money and be more accurate than the 1990 effort which, later checks indicated, missed 8.4 million and double-counted 4.4 million people. Sampling would count more than 90 percent of Americans directly and use those results to estimate those not counted directly.

Congressional Republicans fought that plan, contending that it was unconstitutional and worrying that it would result in increased numbers of people counted in largely Democratic urban areas. Since the numbers are used to allocate seats in the House of Representatives among the states, they feared it would lead to gains for Democrats.

The Supreme Court agreed that sampling did not satisfy the legal requirements for numbers to be used in apportionment.

But the court also left open the possibility of sampling for other Census numbers, which are used for such purposes as distributing billions of dollars in federal funds among states and localities.

In February, the Census Bureau, a part of the Commerce Department, submitted a budget request for $2.879 billion for fiscal 2000 to complete the census. Prewitt said it will now have to seek an additional $1.723 billion in the coming year.

CAPTION: Census Director Kenneth Prewitt attributes increase to court order on count.