A pill version of the drug acyclovir is about to be marketed for use against genital herpes. This drug, which was awaiting Food and Drug Administration approval as this column went to press, could relieve the suffering of the estimated 5 million to 20 million Americans who have genital herpes and the 300,000 new cases each year.

Acyclovir, which was developed specifically to combat herpes simplex, both oral and genital, has been on the market in the form of an ointment since May 1982. It should eventually provide relief from the pain, discomfort and even the infectiousness of most members of this nasty, but almost never life threatening, family of viruses.

The pill verson will be specified for use in healthy people with genital herpes. Once a drug is approved, however, doctors are not restricted in its use.

Ongoing clinical trials suggest that oral acyclovir will be useful against almost the whole panoply of herpes infections, even including those minor but highly publicized outbreaks of the past few weeks that provoked an irrational hysteria and, for no good medical reason, turned a handful of American toddlers into latter-day lepers.

Recently published studies also suggest the use of acyclovir against shingles, the painful rash that can afflict those older than 50 who had chicken pox as children. The most notable recent case of shingles was that of former president Richard Nixon. He joined the other 300,000 people who develop shingles each year. The "excruciating pain" he reportedly experienced weeks after the onset of this common herpes infection suggests to some experts that he may have had a shingles complication called "postherpetic neuralgia" -- the continuation of sometimes agonizing pain long after the rash itself disappears.

And at least one expert on the family of herpes viruses speculates that the former president's discomfort probably could have been relieved, or even prevented, by the prompt intravenous use of acyclovir.

Shingles is, in fact, a recurrence of chicken pox. That common childhood illness -- uncomfortable, but benign in the vast majority of cases -- is caused by the herpes virus called varicella-zoster. By far the most contagious of the herpes family (because it is transmitted both by contact with the rash and through airborne particles), it infects about 98 percent of the population before age 18.

Shingles, known to the medical community as herpes zoster, may not occur for decades after the bout with chicken pox. As with all herpes viruses, the varicella hibernates in nerve cells. As virologist Henry H. Balfour Jr. writes, "The virus survives like seeds of fire in a bed of coals. Sometimes these viral seeds burst into flame as the burning rash of shingles."

Although most of the published research on acyclovir and shingles has reported on trials using injected acyclovir, more recent work suggests that the oral will be similarly effective as well as more easily administered. Acyclovir interferes with the genetic coding of the virus, preventing it from reproducing itself. It does not eliminate the virus from the system -- and therefore is not a cure -- but the drug keeps the virus inactive.

So why hasn't the world rushed to acyclovir? "Well," says Balfour, "I think the manufacturer (Burroughs Wellcome) made a tactical error by pushing the ointment first." Balfour, director of the clinical virology service of the University of Minnesota medical school and author of "Herpes Diseases and Your Health" (with Ralph C. Heussner, University of Minnesota Press; see book review on Page 18), is one of the country's leading researchers on acyclovir and other drugs that fight viruses.

"The ointment is the least effective way to use this kind of drug," says Balfour, "just as it is with antibiotics. The most useful is by injection, the next through a pill and the least effective is the topical cream or ointment."

Because the ointment had only limited usefulness, principally in the first outbreak of genital herpes and less so in recurrences, it was widely -- although unjustly -- dismissed as "just another failure," because, says Balfour, "the track record for antiviral agents has been pretty dismal up to now."

The approval of the pills should turn it all around, Balfour predicts.

Patricia Randall, information officer for the National Institute of Allergy and Infectious Diseases of the National Institutes of Health, says studies demonstrate that in cases of genital herpes, oral acyclovir "is effective in treating both initial and recurrent outbreaks."

Moreover, she says, trials conducted by NIAID's chief of neurology, Stephen Straus, show that taking oral acyclovir continually can prevent recurrences in people who had been plagued by more than a dozen herpes episodes a year. As long as they took the acyclovir pills, there were no recurrences.

However, Randall points out that although there seemed to be virtually no side effects, the long-range effects are unknown. When the daily doses of acyclovir stopped, the recurrences returned, but the manufacturer is recommending that it be used for no more than six months.

Acyclovir has not been tested on pregnant women, but it is being tested on newborns who contracted the virus at birth. Because the immune system of these infants is immature, the virus can grow uncontrollably. But once the child is more than a month old, the immune system has developed enough to control the herpes infection in most children.

"I wondered," says Randall, "why no one asked about acyclovir in terms of those school incidents."

"I think we could say," says Balfour, "that even though it is not technically sanctioned by the Food and Drug Administration, the chances of the herpes in those children responding to acyclovir would be excellent."

"People still think herpes lasts forever," he says, "and that you can't do anything about it. Some people won't even listen. With acyclovir and some other antiviral agents being tested, they're just wrong."