The United States has the technology to provide early warning to contaminants such as PCB, PBB, mercury and Kepone in the food supply, but is failing to use it, an advisory body to Congress said yesterday.

The result, said the Office of Technology Assessment, is certain to be some new and unexpected contaminatin, even though the most complete warning network could not guarantee against all problems.

PCBs and PBBs are industrial chemicals that have found their way into animal feed and human foodstuffs. Kepone is the insecticide that has contaminated Virginia's James River and its fish and shellfish. Mercury is a widely used liquid metal that has found its way into the fish of lakes and rivers.

These and other contamiants -- chemicals, metals and radioactive elements -- are sure to be with us in an industrial society. Many can cause health problems.

The technology to detect many of these problems to advance consists in part of batteries of laboratory tests for mutagens and carcinogens, chemicals that cause either genetic mutations or future cancers or, often, both. Food screeners use such tests to observe any effects on bacteria or on animal or human cells and genetic material.

Any questions raised by such tests might then have to be checked in animal colonies, a process that can take two to three years.

But a warning system using such tests systemcatically, the OTA said, would be more likely to prevent future disasters than the present sketchy and uncoordinated use by regulatory agencies like the Food and Drug Administration, the Agriculture Department, the Environmental Protection Agency and their many state counterparts.

In the recent PCB contaminiation of animal feed, poultry and eggs in the west, the report said, ETA analyzed air and water samples (with negative results), but did not give its results to state agencies seeking similar information. When the Idaho Agriculture Department learned of the contamination, it failed to tell the Idaho Health Department.

A survey of 32 states and 10 federal agencies found there were 243 "contamination incidents" in the United States between 1968 and 1978, touching every region, involving "all kinds of food" and often lacking full information.

What is needed, said OTA, is not only systematic tests of foods and chemicals but also "a clear authority to coordinate activities" of federal and state agencies, including coordinating communication.

In response to these needs, the Ota said, Congress might do one or a combination of three new things:

Amend the Food, Drug and Cosmetic Act to give the FDA greater power to detect the regulate harmful contaminants.

Establish a "national investigatory monitoring system": a chain of laboratories using new methods still not found in most federal and state laboratories.

Designate a lead agency or establish a new center to seek, evaluate and distribute information to affected states and other agencies.

As one immediate step, the OTA said, Congress might at least authorize a two-to-five-year pilot program to see how productive and practical total monitoring of the food supply might be.

The OTA made its report to the House Commerce Committee, four of whose members requested it. Oversight and investigations subcommittee Chairman Bob Eckhardt (D-Tex.) said the report shows the need for "immediate federal review of our ability to control harmful substances."