Many Americans need far fewer cancer tests than their doctors have been recommending, and most do not need an annual physical to check for cancer until after age 40, the American Cancer Society has concluded.

In a major change of policy, the society said yesterday it is dropping its recommendation that certain cancer tests be given everyone every year. Among these are breast exams and Pap smears, which it no longer recommends for all women yearly, and annual X-rays, which it calls unnecessary for symptom-free persons.

The changes were prompted by wide medical opinion that too many tests may be finding only a negligible number of cancers at great dollar cost.

A sparer, better designed test schedule may find more cancers and also produce more cures, cancer society officials maintained.

The society now recommends for all well, sympton-free persons:

A cancer checkup and health counseling every three years for everyone over 20, annually for all over 40.

Continued monthly breast self-examination by women over 20. Breast examination by a doctor every three years from ages 20 to 40, then annually. One baseline breast X-ray between 35 and 40, then an annual X-ray after 50.

A Pap test for cancer of the cervix (lower womb) every three years (if two exams a year apart have been negative) for women 20 to 65 and younger, sexually active women. A pelvic exam every three years from 20 to 40, then every year. A single test of an endometrial (womb lining) sample at menopause for women at high risk because of obesity, use of estrogens or medical history.

An annual manual rectal examination by a doctor with a single guaiac (chemical) slide test of a stool sample for everyone over 40. More extensive slide testing annually after 50. Sigmoidoscopy (an instrument probe of the rectum, often called proctoscopy) every three years after 50, if two exams a year apart have been negative.

The recommendations were based on opinions by experts in all fields of cancer. They reviewed each cancer's frequency, the age when it usually appears, and the good or harm each test may do.

Unneeded X-rays, for example, waste money and expose the patient to radiation unnecessarily.

While the cancer society has not specifically been urging an annual physical, its slogans -- get "periodic" or "regular" physicals and fight cancer "with a check and a checkup" -- have "very much implied" the need for annual physicals, said Dr. Sol B. Gusberg of Mount Sinai Medical Center, New York, the society's president.

Today, he said, "we have to ask some better questions," like what is most cost-effective, what is most effective medically, what is most practical?

"These are general guidelines," he added. "Some people are at higher risk. Consult your doctor to see if they suit you." High risk persons include women with family histories of breast cancer or, for cervical cancer, early sex and multiple sex partners.

"Some individuals and some physicians may quite logically have different priorities," said Dr. Arthur Holleb, cancer society medical director. "No one recommendation is right for everyone."

While the new recommendations are aimed mainly at finding cancer, they are designed to mesh to some degree, at least, with the latest views on general medical checkups.

A panel of the Institute of Medicine at the National Academy of Sciences has recommended:

A complete checkup for all at age 18 or soon after.

Starting at age 25, visits every five years.

After 40, visits every two and a half years with the alternate visits less thorough.

Visits every two years after 60 and every year after 75.

How does a person know when a cancer checkup is careful?

The examining doctor, said Gusberg, should always examine the "oral cavity, neck and thyroid gland, other glands and lymph nodes, breasts, abdomen, the pelvis in women and testes in men, do a rectal exam and a slide test of the stool -- and look at the whole body and skin" from top to bottom.