At least 638 waste disposal sites around the United States pose potential public health hazards and many of the sites are unknown to people residing nearby, federal officials said yesterday.

Moreover, the nation's top waste management official said there is little chance that much will be done about the sites because a new federal program designed to deal with toxic waste disposal does not cover existing sites.

The Environmental Protection Agency yesterday released the first nationwide inventory of hazardous waste sites. The report - spurred by recent news accounts of deadly waste seeping from dump sites into homes and water supplies - says at least 32,254 sites "may contain hazardous waste in any quantity which now or potentially could cause adverse impact on public health or the environment."

The report singles out the northeast and the Far West as the two areas where the hazardous waste dumping is the worst. But Thomas Jorling, assistant EPA administrator for water and waste managements, said yesterday that "our degree of confidence in this survey is not high." He said that the EPA list may be incomplete and that some sites listed may no longer exist.

"We have a chicken and egg dilemma," Jorling said. "We know we don't have the resources to identify the problem, but before Congress can act to do something we have to know the extent of the problem."

Jorling listed several examples of EPA's hazardous waste disposal problem:

The cost of cleaning up the highly publicized Love Canal dump site near Niagara Falls, N.Y., is likely to run more than $40 million, Jorling said. So far, federal and state sources have put up $10 million, which he said means that much of the problem will go untreated.

At Charles City, Iowa, where potentially toxic wastes from a drug plant are leaking into the Cedar River water supply, EPA has received a $40 million cleanup estimate. "We jury rigged an identification procedure but we can't do much more than watch it happen because we haven't got any money," Jorling said.

In Ambler, Pa., a 10-block-long pile of asbestos waste is blowing into a playground and the Schuylkill River, which runs through nearby Philadelphia. "Final remedial action is, so far, unplanned," the EPA survey says.

The survey lists only two sites in the metropolitan area. In the Little Elk Valley in northern Maryland, the survey notes an unidentified study has put the cancer level at 30 times that of the surrounding country's level. The other site, a dump near Elkton, Md., has also drawn health complaints from nearby residents. No final federal action has been taken at either site, according to the survey.

"We have no way of systematically going to any of these sites and finding out what's there and what can be done about it," Jorling said.

The EPA inventory estimates that 30 to 40 million tons of hazardous waste is being produced each year and nearly all of it is being dumped so that it won't meet future environmental standards. They survey specifically identifies 103 sites it says are "current threats."

Jorling said one federal estimate placed the cleanup cost for each site at an estimate $20 million. "But," he added, "that doesn't really give an accurate picture. At some of these sites we don't know the cleanup cost because the remedy is not yet technically known."