A new birth control method, designed to last longer, cost less, and be safer to use than the conventional pill, has been successfully tested in Mexico and will soon begin clinical tests in the United States.

In the new method, women get shots once every six months. The same hormone commonly contained in contraceptive pills is used, but it is encased in thousands of capsules the size of pinpoints. Once in the body, these capsules release their contents by a steady diffusion, thus slowly releasing a constant amount of the hormone into a woman's body. After the capsules finish releasing their hormone, they dissolve into chemicals normally found in the body.

"If you take a birth control pill orally," said Dr. Lee Beck of the University of Alabama, leader of the team that developed the new method, "you get about 50 times the dosage you need every time you take an oral contraceptive. You get a very high level of [hormones] in the blood immediately after absorption, and then the level decreases every hour. The amount you really need is the amount obtained 15 or 20 hours after you take the one big dose."

This high dosage, plus the inclusion of the hormone estrogen in the pill, are probably causes of the many suspected side effects of using the pill, Beck said. The pill is believed to contribute to hypertension, is suspected of helping to trigger cancer, and is suspected of giving women predisposition to stroke, among other side effects.

The new method avoids both the high doses and the use of estrogen. Estrogen is put in pills largely to help induce bleeding for a menstrual pseudo-period which occurs during the one week per month that the pill is not taken, according to Beck. In the new contraceptive only the basic "progestational" compound that stops ovulation is used.

As for the dose, Beck said, "With controlled release, we adjust the rate so that the level is constant and unchanging," he said, "and at a far lower dose than oral contraceptives must use."

Beck said he believes the new contraceptive will be most useful in undeveloped countries where "people are not educated to the habit of taking pills, where women never see a gynecologist, and where people have little regular access to doctors. In these countries there has to be a great desire to have an injectable contraceptive, which can be given by the local pharmacist as most other shots are," Beck said.

One difference with the new method is that women may have no menstrual periods at all, or expereince only sporadic, spotty bleeding. "I don't know if women in this country will accept the complete absence of periods or will be willing to have the inconvenience of spotting," Beck said. "But we are providing an alternative, and one we expect will probably be safer and cheaper."