Ralph Nader and an ex-federal insurance administrator yesterday called on the Justice Department to determine if the insurance industry is illegally boycotting certain businesses and professions that need liability coverage.

The industry has manufactured the current shortage of liability insurance to force state insurance commissioners to approve higher premiums and coerce lawmakers into reducing legal liability, Nader and J. Robert Hunter charged at a news conference.

In the past several months, scores of businesses and professionals have been affected by rising premiums and declining availability of coverage. Those who have been hit include doctors, lawyers, architects, municipalities, day-care centers and many others.

"The insurance industry is going on strike in order to extort higher rates from consumers and businesses and force the legislatures to restrict the personal injury rights of millions of Americans," Nader said. "This is done, jointly, by means of a boycott."

Evidence for the boycott cited by Nader and Hunter, president of the National Insurance Consumer Organization, included recent statements by reinsurers warning state regulators that they would withdraw from certain markets en masse if the regulators did not approve more narrow insurance policy forms. Reinsurance companies assume some of the risk underwritten by insurance firms.

Insurance companies also were accused of withdrawing from certain areas of coverage, such as that for day-care facilities and nurse midwives, even though they had very little loss experience in those lines.

Under federal law, the insurance industry is exempt from antitrust rules unless it is involved in boycotts or intimidation, said Mark Sheehan, a Justice Department spokesman. He said the department will look into the complaint to see if a full-scale investigation is called for, but stressed that it has arrived at no conclusions yet.

Responding to Nader's accusations, however, spokesmen for the insurance industry said the insurance squeeze is the result of tremendous losses, $3.8 billion in total, suffered last year by the property-casualty business. The property-casualty business includes all lines of insurance except for health and life insurance.

"The suggestion that we're raising rates to influence the legislative process is nonsense," said Marc Rosenberg, a vice president at the Insurance Information Institute, who noted that insurance rates are regulated by state agencies.

Rosenberg and Dennis Connolly, an executive at the American Insurance Association, said there were certain lines of insurance, such as protection for toxic waste removal, for which it is impossible to calculate risk because of expanding notions of legal liability in the courts.