The American woman's need for regular Pap smears to prevent cervical cancer -- which researchers now believe is transmitted much like a veneral disease -- was underscored yesterday by a national panel of health experts.

The experts said that a woman's sexual behavior, more than any other factor, determines whether she falls in a group with a high risk of contracting the cancer. The high-risk group, the experts said, probably needs yearly Pap smears.

The panel's report, issued yesterday at the close of a conference at the National Institutes of Health in Bethesda, failed to resolve a debate between gynecologists and the American Cancer Society over how frequently a smear test is desirable or useful.

The gynecologists' professional organization still advocates annual Pap smears for every woman. The cancer society, however, said last February that a woman who has had two normal smears needs the test only every three years.

Since the Pap smear began to gain widespread acceptance in the 1940's, studies show that it has contributed to a dramatic drop in the death rate from cervical cancer in the United States and other developed countries.

To perform the test, a doctor scrapescells from the cervix or mouth of the uterus. The cells are spread on a slide, stained, and examined for the presence of cancer or its precursors.

The conference report makes the following recommendations:

A woman who has never had sexual intercourse need not receive Pap smears, unless she was exposed to estrogen before birth or has some other unusual risk factor for developing cancer of the sexual organs.

A woman should begin to get regular Pap smears soon after she becomes sexually active, regardless of her age.

If her first Pap smear is normal, she should be tested again a year later.

If the second Pap smear is also normal, the decision of how often the test should be repeated -- whether at one-, two-, or three-year intervals -- should be left to each woman and her doctor. It must take into account her individual risk of developing cervical cancer. Women at high risk are those who first had sexual intercourse before age 18, those who have had multiple sexual partners, and those in low socioeconomic groups.

Women who have had two normal Pap smears after age 60 need not continue to be tested for cervical cancer.

Although the death rate from cervical cancer in the United States has been decreasing steadily, the disease killed 7,400 women in 1979. Dr. Maureen Henderson, the panel's chairman, estimated that this year 45,000 American women will be found to have very early cervical cancer, and 16,000 more will be found to have cancer that has spread beyond the outer layer of the cervix.

A woman's risk of cervical cancer is so closely tied to her sexual behavior that doctors are convinced some casual factor for the disease is transmitted by intercourse. The Herpes virus or some other virus may be implicated, since cervical cancer victims have higher rates of infection with Herpes and other kinds of infection.

Cervical cancer "behaves very much like a venreal disease," said Dr. Anthony Miller, director of epidemiology for the National Cancer Institute of Canada. Studies have shown that nuns virtually never get it, while one study found that up to 8 percent of prostitutes become victims.

Thus, the more sexual partners a woman has had, the higher her risk of developing cervical cancer, just as a heavy smoker has a greater chance of getting lung cancer, Henderson said. Becoming sexually active early and having a first pregnancy early also increase a woman's risk.

Other factors once thought to increase risk -- like using birth control pills or having intercourse with an uncircumcised man -- have not stood the test of further research, according to a report presented to the panel by Dr. Barbara S. Hulka of the University of North Carolina.

The ability of the Pap smear to detect cancer early has been so well publicized that in 1976 a Gallup survey found that 82 percent of American women between the ages of 18 and 34 had had the test at least once. More than 34 million Pap smears are performed yearly, according to the National Center for Health Statistics.

However, the original recommendation for yearly Pap smears was made arbitrarily, since at the time the test was introduced no one knew how often it should be administered. Research done since then has shown that cervical cancer grows very slowly.The earliest stage of the cancer, during which it is easily removeable and 100 percent curable, lasts eight to thirty years on the average and very rarely lasts less than three years.

These studies prompted a Canadian study group in 1976 to issue recommendations for less-frequent Pap smears -- every three to five years, for women at low risk -- after two initial tests had been negative. The American Cancer Society made its own similar recommendation last February. The society argued that screening women every three years would still pick up virtually every case of cervical cancer before it had spread, and would greatly reduce the cost of finding cases. Under an annual screening program, about 25,000 women must be tested to find one cancer.

The cancer society's new recommendation prompted an impassioned defense of the annual Pap smear by the American College of Obstetricians and Gynecologists. A policy statement issued yesterday by the college's executive board said lengthening the interval between Pap smears "inevitably trades lives for dollars."