Starting today, couples applying for a marriage license in Illinois or Louisiana must prove that they have been tested for the AIDS virus.

Under controversial new laws, the first of their kind in the nation, engaged couples are required to provide to the county clerk a certificate signed by a licensed medical doctor stating that both individuals have been blood-tested within the past 30 days for evidence of the human immunodeficiency virus (HIV), which causes acquired immune deficiency syndrome.

The certificate does not disclose the results of the HIV test. It specifies only that the two individuals have been tested and have been informed of their own and each other's HIV test result. A positive result will not in itself keep anyone from legally obtaining a marriage license.

HIV testing, particularly mandatory testing, is controversial because of its cost and concerns about the confidentiality, accuracy and usefulness of the results. Most medical authorities favor voluntary testing instead, arguing that mandatory testing of relatively low-risk groups would be expensive and largely ineffective against the spread of the fatal disease.

"The payoff is going to be awfully low," said Dr. Martin E. Levy, administrator for preventive health services in the Commission of Public Health in the District of Columbia, which is opposed to mandatory testing. He also expressed concern about the difficulty of protecting confidentiality of test results.

Mandatory testing to pinpoint HIV-positive individuals might make more sense, Levy said, if effective drugs were available to treat HIV and prevent it from developing into AIDS. "Unfortunately, we're just not at that stage yet," he said.

Under the Illinois law, doctors are required to report all positive test results -- indicating infection with the AIDS virus -- to state or local health authorities. To preserve confidentiality, such cases are to be reported by age, sex, race and risk factors, but not by name. The Louisiana law does not require reporting of HIV-positive cases.

An early draft of the Illinois law was opposed by the state Department of Public Health because it required the state to bear the cost of the premarital testing. That cost, estimated at several million dollars, would have exceeded the state's budget for AIDS education. Under the revised law signed into law by Gov. James R. Thompson (R) Sept. 21, the cost of the required premarital AIDS test -- estimated to range from $12 to $100 -- must be borne by the applicants.

State health officials estimate that of the 200,000 individuals expected to apply for a marriage license in Illinois this year, about 400 will test positive for HIV on the basic ELISA blood test, and about 80 will be confirmed as positive on the more reliable Western blot test.

The AIDS virus can be spread from one person to another through sexual relations or sharing of intravenous needles or syringes, or from an infected mother to her newborn.

The federal Centers for Disease Control and Surgeon General C. Everett Koop have opposed mandatory testing in favor of voluntary testing, combined with public education and counseling.

Within the Reagan administration, Secretary of Education William J. Bennett and White House aide Gary Bauer have led the call for required testing. President Reagan himself has called for required AIDS testing of marriage-license applicants, prisoners and would-be immigrants. Currently, the AIDS virus test is required of blood donors, military recruits and active-duty personel and State Department Foreign Service officers.

A cost-benefit analysis of mandatory premarital HIV testing, reported in the Journal of the American Medical Association last October, concluded that such testing on a national basis would be "a relatively ineffective and inefficient use of resources."

It would detect fewer than 0.1 percent of infected individuals at an annual cost of more than $100 million, according to researchers from the Harvard School of Public Health.