ASHINGTON, Jan. 24 — Federal health officials said today that they were planning to distribute more than $1 billion to help states improve their defenses against a biological attack but that the bulk of the money would be withheld until the states submitted detailed preparedness plans.

The money is part of nearly $3 billion the Department of Health and Human Services will spend this year on bioterrorism preparedness, roughly 10 times what the agency spent last year. Congress appropriated the additional money after the Sept. 11 terrorist attacks and the October anthrax attacks.

"Anybody that has been in the public health arena has wanted resources available to build a strong local and state public health system," Tommy G. Thompson, the secretary of health and human services, told reporters this afternoon in announcing the department's plans. "We've never been able to get the political or financial resources to do that. We have it now."

State health officials said today that they were eager for the money but were concerned that it would not last. "Yo-yo funding has been the history of public health," said Dr. Georges C. Benjamin, president of the Association of State and Territorial Health Officials.

Dr. Leslie M. Beitsch, the health commissioner in Oklahoma, said, "I think it's a very significant commitment, but the question then becomes, is it a long-term commitment?"

Mr. Thompson indicated today that it would be. He said President Bush intended to ask Congress for an increase in bioterrorism spending in 2003. Mr. Thompson would not specify the amount, but he said, "people will be happy."

The anthrax attacks, which killed five people and sickened more than 12, exposed holes in the public health system. Some states lack federally trained epidemiologists, the disease detectives who investigate outbreaks. Communication needs improvement; in some regions, health officials lack electronic mail or pagers and cannot be reached quickly in an emergency. Public health laboratories are understaffed. Hospitals lack coordinated plans for responding to a biological attack.

To help states devise plans, the federal health agency intends to release $200 million now. The rest will be distributed after the plans are approved. Mr. Thompson said his agency was devising a formula to determine what each state would get.

How much money states need is in dispute. The American Hospital Association estimated that hospitals alone would need $11 billion.

But federal health officials called the $1 billion a giant leap forward, saying it was roughly a twentyfold increase in what states had received in previous years.