THE JOB of cleaning up the chemical waste dumps is evidently going to be harder than it looked at first. It's going to take longer, cost more money and require technology that hasn't yet been developed. Perhaps, as the congressional Office of Technology Assessment now suggests, it's time to consider a change in basic clean-up strategy.

It's been a little over four years since Congress, responding to the first alarms about the chemical dumps, established the Superfund to pay for the cleanups and told the Environmental Protection Agency to manage it. This year Congress will reauthorize Superfund and, in preparation, two House committees asked the OTA to have a look at the operation so far.

OTA says that the number of dumps requiring action is going to be very much larger than the Environmental Protection Agency's current estimate -- perhaps five times as large. But it warns against the American habit of resorting to crash programs. For both technical and economic reasons it will be impossible to correct all of the sites permanently within even as long a period as 20 years. Instead, OTA proposes a two-step plan. For the next 15 years, the government's work would be directed mainly toward stop-gap remedies of immediate health risks, accompanied by a wider and more complete survey of these hazards. In many cases it might mean merely storing dangerous wastes until the chemical engineers devise ways to dispose of them safely. Much more effort is going to have to go into research and into developing an adequate corps of people trained for this field. Only after many years, around the turn of the century, will the EPA be equipped to begin the phase of permanent and complete cleanup of the these dumps.

And it will be expensive. OTA offers a rough guess of $100 billion over many decades -- a figure presumably intended only to warn that the costs are likely to run well beyond anything that Congress has yet contemplated. Superfund's money currently comes mostly from a tax on petrochemicals. But one industry can't, and shouldn't, bear the weight of the expansion that may now be necessary.

OTA has put the right questions before Congress, including the hardest question of all: how clean is clean? Congress rarely deals well with that one. It always wants to say: completely clean, and completely safe. But that, OTA plainly tells its congressional masters, isn't realistic. If perfection isn't practicable, what ought to be the standard? Here's a suggestion: as long as each additional dollar spent on Superfund buys more health protection for the public than a dollar spent on other environmental programs, more money for Superfund will be well justified. By that rule, OTA says, Superfund is likely to have a long life ahead of it."