Insurance companies, employers and some group health organizations are moving more aggressively to limit their financial exposure to AIDS by requiring blood tests of potential policyholders and by curtailing or eliminating coverage for the disease.

An increasing number of companies are requiring applicants for individual health and life insurance to take blood tests that detect infection with HIV -- the human immunodeficiency virus that causes AIDS. Only the District and California prohibit by law HIV testing by insurance companies, although officials in about a dozen other states say they oppose the practice. In recent months, the insurance industry has succeeded in persuading courts in New York and Massachusetts to overturn rulings by insurance commissioners in those states that would ban testing.

Companies are using other measures to try to limit AIDS claims.

Beginning Jan. 1, the George Washington University Health Plan will limit coverage for prescription drugs to $3,000 per year for persons covered under its high-option plan, which includes AIDS patients. The university's hospital has treated more than 268 AIDS patients since 1982, more than any other hospital in the area.

GWU officials say they are seeking to control costs that result from expensive new drugs, including azidothymidine, or AZT, the only drug approved to treat AIDS. A year's supply of AZT, believed to be the most expensive widely used prescription drug, costs $10,000 to $12,000.

In recent months, Connecticut-based Aetna Life & Casualty, one of the nation's largest insurance companies, has substantially increased HIV testing. Beginning Oct. 1, Aetna ordered that all potential individual policyholders in New York and California be screened for AIDS. Although California bars the HIV test, it permits other methods of screening.

Last spring, Preston Trucking Co., a self-insured firm headquartered in Preston, on Maryland's Eastern Shore, imposed a $50,000 lifetime maximum for medical expenses related to AIDS. Current estimates of the cost of care range from $22,000 per year to a lifetime amount of $147,000. The company does not limit reimbursement for heart attacks or injuries that result from a car accident, either of which often is more costly than AIDS.

"AIDS is a very hot issue for us," said Deborah Chase, a spokeswoman for the American Council of Life Insurance and the Health Insurance Association of America, the industry's trade associations. "There is an increasing awareness in the industry that AIDS is a growing problem. For some companies it is ultimately a question of solvency."

The insurance industry argues that it should be allowed to screen for AIDS as it does for other diseases. AIDS, industry officials argue, presents an unprecedented risk to the industry. A recent report by the Society of Actuaries predicts that without widespread screening, premature-death claims could total $64 billion by 2000.

"Insuring a person who has tested positive is like someone whose house is on fire trying to buy a homeowner's policy," said Aetna spokesman Mark Goodin.

Critics argue that a positive test renders someone uninsurable and deprives them of quality care. They contend that the cost of AIDS will be shifted to taxpayers, who will end up paying for AIDS through Medicaid and public hospitals.

"Insurance is not like any other industry, because without it you don't have access to decent health care," said Peter S. Arno, assistant professor of health care administration at The City University of New York. "The industry is given a lot of tax benefits because it's not just a business, it performs certain social functions in our society."

Benjamin Schatz, director of the AIDS Civil Rights Project for the National Gay Rights Advocates, a San Francisco law firm active in the area of AIDS and insurance, said, "The industry has repeatedly opposed national health insurance because it insists it can handle health costs better. Well, there are risks to insurance companies if people are not tested and risks to society if people are not insured."

There is little agreement about how much AIDS will cost, although industry officials and critics say that AIDS is expensive, largely because most cities rely on unnecessary and expensive hospital treatment rather than developing a less expensive network of home care services. One widely cited study projects that by 1991, AIDS will absorb $8.5 billion in medical costs.

"There is no question that AIDS will be a large expense to this nation," said Willis B. Goldbeck, president of the Washington Business Group on Health, a national nonprofit organization subsidized by large corporations. "But the fact remains that smoking costs more than AIDS ever will."

A 1985 study by the congressional Office of Technology Assistance, which is now studying AIDS and insurance, says that smoking costs American business $43 million in lost productivity and $22 billion in medical expenditures annually.

"The average cost of a liver transplant is $240,000, and the trend for insurance companies is to give more, not less, coverage for transplants," Goldbeck said.

Concern about costs and regulation by state insurance officials has led many companies to self-insure, according to Arno. Self-insured companies assume ultimate financial responsiblity for claims, even though their health plans are often administered by insurance companies. Self-insured plans are exempt from state regulation, and companies are free to determine whether -- or how much -- they will pay for particular diseases or conditions.

Preston Trucking Co. decided this year to impose a lifetime $50,000 maximum for AIDS even though there have been no AIDS claims from Preston's 1,600 workers.

"We didn't know what was coming, and we wanted to be prepared," said Robert Thompson, the company's director of insurance. "We do not think it's discriminatory. AIDS is such an experimental thing, we're just saying, 'This is all we'll pay for.' "

The Laborer's Health and Welfare Fund for Southern California, which insures 20,000 construction workers and their families, excludes AIDS claims except for people under age 13 and those who contract the disease through a blood transfusion.

"Why is it so terrible?" asked John Miller, the fund's attorney. "Isn't it better than excluding all AIDS coverage?"

Dr. John Ott, administrator of the GWU Health Plan, says that while current AIDS claims are "manageable," officials decided to limit the benefit for prescription drugs to $3,000 because of concern about drug costs.

"There are many insurance companies that don't have a prescription benefit at all," he said. "The $3,000 figure is 40 to 50 times what the average person spends on drugs in a year."

Ott declined to disclose the number of AIDS patients enrolled in the plan or to specify the amount the plan has paid in AIDS claims.

"We're not trying to drive AIDS patients out," he said. Ott suggested that those who cannot afford to spend $8,000 a year for AZT might be able to get additional funds through state governments or might consider switching to less-expensive experimental drugs.

That is no solution for Ray and John, federal employes in their midthirties who have taken AZT for the past year. Because each is paid more than $21,000 a year, they do not qualify for supplemental AZT funds allocated by the District goverment.

Both men, who requested that their last names be omitted, have been insured by GWU for more than five years. Each says he will switch health plans reluctantly because he believes that he needs AZT to survive. The drug is not a cure for AIDS but does prevent replication of the virus and has been successful in staving off infections and prolonging the lives of AIDS patients.

"What's $1,000 per month compared to a six-week hospital stay for an infection that could kill me?" said Ray. "It's crazy, because GW will still pay for hospitalization, but not for the drug that can help prevent it. I think they could have increased premiums rather than just concentrating on slashing the drug benefit."

John, whose salary is $22,000, says he has exhausted his savings paying for AIDS and cannot afford $8,000 a year for AZT.

"I've been with GW for eight years and I like my doctor, and I had a vested interest in continuing," said John. "I'm really worried about finding good care somewhere else."

In some cases, concern about AIDS has caused insurance companies to designate occupations -- including hairdressing, interior design and restaurant work -- as "high risk." Several companies have stopped writing policies for people employed in those fields.

"In the past two weeks, I've gotten calls from two restaurant owners who couldn't get insurance and a doctor who couldn't get group health coverage for her employes because the company was worried about needle sticks," said Mark Senak, legal director of New York City's Gay Men's Health Crisis, the nation's oldest and largest AIDS organization.

Thomas B. Stoddard, executive director of the Lambda Legal Defense and Education Fund, a gay rights law firm based in New York City, said he had trouble getting disability insurance last year when he joined the firm.

"The broker said I should list NYU {New York University}, where I teach part time, as my employer, rather than Lambda, and that I should say that I had been married," Stoddard said.