Federal regulators are poised to approve a long-acting contraceptive that public policy experts say has generated more excitement and uneasiness than any birth control method since the pill.

Known as Norplant, the new device prevents pregnancy by using one of the same synthetic hormones found in oral contraceptives. But instead of being taken daily in pill form, the hormone is delivered in a steady dose by six matchstick-sized capsules implanted under the skin of a woman's upper arm, offering convenient and continuous contraception for as long as five years.

A Food and Drug Administration panel concluded last year that there were no outstanding questions about the drug's safety or efficacy. The drug's developer, the nonprofit Population Council, says it has submitted all relevant data to the FDA, and industry analysts say approval is imminent. But as it nears approval, Norplant has become the subject of a spirited debate among women's health experts and social policy thinkers.

The focus of the debate is the fact that, once the implant is in place, its effectiveness in preventing pregnancy does not depend on the user's behavior. While birth control pills can be forgotten and diaphragms can be left in a drawer, Norplant is inserted by a doctor and, once implanted, stays in place until it is removed by a doctor. Meanwhile, it prevents conception regardless of accident, impulse, forgetfulness or any of the other factors that plague traditional birth control methods.

This fact, experts agree, makes Norplant ideal for groups of women -- such as teenagers or drug addicts -- who have a troubling rate of unwanted pregnancy and for whom existing methods of contraception are often unsuitable. But the implant's potential effectiveness among such groups has also raised troubling questions.

For instance, do Norplant's advantages mean the government should, for the first time, get into the business of promoting a specific contraceptive method? Will the device encourage courts and employers to take contraceptive decisions out of the hands of some women? In short, is this a technology that will enhance a woman's reproductive freedom or curtail it?

"With Norplant we are faced once again with technology outpacing our ability to fashion an ethically based system to deal with it," said Gary Bauer, president of the Family Research Council.

With currently available methods, the decision to use birth control rests ultimately with the individual. But with the approval of Norplant, some policy experts point out, a third party such as a court or an employer may be able to enforce -- at least in the short run -- its independent determination that a woman should not get pregnant.

"It is only a matter of time before a judge in some community orders a Norplant implant for some woman who is engaged in what the judge believes could be dangerous or risky behavior for a fetus," said University of Minnesota bioethicist Arthur Caplan. "I promise it will happen."

Norplant contains the hormone levonorgestrel, a chemical also used in some of the newer, safer formulations of birth control pills. As a result, it shares some of the side effects, such as weight gain and headaches. It also produces irregular bleeding in some users.

But none of these problems is considered serious, and the drug is said to be 99 percent effective for up to five years. Insertion and removal of the capsules containing the hormones require a simple, 10-minute surgical procedure in which a doctor administers a local anesthetic and makes a small incision in the skin. Once the capsules are removed, a woman can regain full fertility within two months.

In clinical trials of the drug, 90 percent of women who used it said they were satisfied. Early experience with it in other countries has been overwhelmingly positive. Norplant appears so appealing, in fact, that it has inevitably attracted attention as a possible birth control method for women who do not otherwise use any artificial contraception.

Urban Institute senior fellow Isabel Sawhill, for example, floated the idea in a recent essay that all girls, at puberty, should be encouraged to use Norplant. The benefits, she said, would be considerable, protecting hundreds of thousands of people who do not now use birth control.

"If women were universally protected, the decision to have a child would become a conscious choice -- decoupled from the dictates of biology, hormones and peer pressure," Sawhill wrote.

Along the same lines, American Enterprise Institute scholar Douglas Besharov met with national drug policy director William J. Bennett last spring to propose that Norplant be made available to poor, inner-city women as part of the war on drugs.

"Norplant looks to me as if it is one small solution to part of the problem of drug-addicted infants," Besharov said. "These are sexually active people. . . . It would be useful and constructive to empower them" to avoid getting pregnant.

These suggestions make some experts uneasy. Conservatives, for example, worry that government intervention might be construed as an endorsement of teenage sexual activity. Others question whether giving teenagers the technical means to avoid pregnancy represents anything more than a cosmetic solution to the problem of early childbearing.

"If we were really interested in the welfare of people, we would start teaching them about how to form relationships, what loving is all about," said Michael Burnhill, a researcher at the Robert Wood Johnson Medical School in New Jersey. "Even if people didn't get pregnant {with Norplant}, they might still wipe themselves out with chronic herpes or HIV {the AIDS virus} or Chlamydia."

A more serious concern expressed by some experts is that promoting Norplant -- even if such promotion stresses the voluntary use of the drug by women -- will amount to a kind of social engineering.

"The whole thing smacks of the paternalistic domination of women that existed back in the '40s and '50s . . . ," said Katherine LaGuardia, director of the division of women's health at New York Hospital. "It should not be marketed as a device to reduce {the number of} drug-addicted babies. It's dictating reproductive behavior in the same way that the right-to-life contingent does on abortion."

Caplan predicted that the line between promotion and coercion is almost certain to be crossed with Norplant, if not by government administrators then certainly by the courts or private industry.

In a case now before the Supreme Court, a company has been sued because it refused to allow women of childbearing age to work in one of its plants. The firm said the lead levels on the factory floor were so high that they might damage unborn children, and the firm could not guarantee that none of its fertile females would become pregnant.

"Imagine this case two years from now," said Caplan. "Then the company would say, 'You can work, but you have to take Norplant.' "

"This is a wonderful drug," Caplan added. "But we need to have an agreement that we will not force it on anyone. We can encourage people. We can cajole them. But I hope we never force them to take this."