Once she sang with the D'Oyly Carte Opera Company in London, groomed for such Gilbert and Sullivan heroines as Mabel or Josephine or Elsie Maynard.

Her husband was a successful business executive.

But it all began to fall apart. As a matter of fact, Angela Kilmartin now recalls, it started on their honeymoon.

It was her bouts with chronic cystitis -- twice a month or more for five years -- that wreaked havoc with her sex life, destroyed her promising career and eventually transformed this proper English lady into a zealous crusader. In the past decade she has, virtually single-handed, wrenched discussion of woman's most common vaginal and urinary complaints out of confinement to clinics and doctors' offices and had them splashed across the front pages of London's popular press.

On the TV talk shows of at least two continents she has -- she will tell you cheerfully -- "vented her anger and spite" on a medical community that left her abandoned, miserable and contemplating suicide. She is outspoken about the prudery that censors discussion of simple techniques that could prevent cystitis in many cases, and about the "popular" aspects of western culture -- such as tight jeans -- that promote this common affliction.

She knows she's in trouble with Gloria Vanderbilt on that one, but she doesn't care.

"Ask any doctor," she shrugs, "they'll tell you that if (skin-tight) jeans were off the market, they'd see fewer (cystitis) patients. . . ."

In a credible U.S. southern accent, she mimics a talk-show host who complained to her, "But ah jus love mah girls in tight jeans . . . they look so se-e-xy."

Her rejoinder: "Take your choice -- having them look that way or be that way."

Other offenders are underwear made from synthetics, so-called "feminine" preparations, sprays and even tampons.

Cystitis is a catch-all phrase for a number of more or less agonizing female complaints caused by a variety of things from poor hygeine to inadequate sexual foreplay. (Even minor irritation of vaginal tissues can induce infection.) Cystitis may be an infection in vagina or urinary tract, or an inflammation. It may respond to antibiotics, or a glass or two of water a few times a day. It may come at age 5, or not until 75. It may occur once in a lifetime (and for a few lucky souls never at all) or it may recur and recur and recur.

Sometimes nothing seems to help. (Reserved for Kilmartin's particular contempt are doctors who do repeated dilatation procedures in usually futile efforts to cure stubborn cases.) She does recommend, however, an initial doctor's visit for a urine test to narrow down as much as possible the source of the trouble.

Kilmartin figures that about one out of three American women and girls suffer from cystitis -- about the same in England -- but nobody keeps track. "More common," she sniffs, "than the common cold, and nobody's counting."

After some years of running a hotline in England for cystitis sufferers and an organization called U & I (both for you and I and Urinary Infection), she wrote her first book in 1972.

Now her second book, Cystitis (Warner, $6.95) is out in paperback. It is basically a self-help manual for chronic victims of the disorder with hints for preventative strategies.

Kilmartin no longer runs the hotline, but divides her time between Saudi Arabia, where her husband is head of National Cash Register Co., and Europe and North America.

The message she most wants to circulate is what she believes saved her -- after five years and visits to scores of doctors. It was this: Be sure and urinate after having sexual intercourse. Her problem, and that, she believes, of millions of others, was the ubiquitous bacterium E. coli, the intestinal germ that causes such trouble in the urinary tract.

Some other explicit Kilmartin musts:

Wear exclusively cotton underwear.

Wash before and after sex, and have your partner do likewise. (But never apply soap directly to the female genital area.)

Use sterile jelly for lubrication if an outside agent is needed.

Avoid chemicals. For example, never wash a little girl's hair in the bath. Avoid bubble baths, colored toilet tissue, sprays and deodorants.

Avoid (as much as possible) tight clothing like jeans and pantyhose.

For those who have had E. coli established as the offending bacterium, she offers a strategy which, she says, can short-circuit an attack:

Get a urine sample to your doctor.

Drink water or water-based liquids (no concentrates): first, 2 cups of water mixed with a teaspoonful of sodium bicarbonate to counter the acidity of urine; then, every 20 minutes for the next 3 hours, a cup of water. Repeat the teaspoonful of bicarb about once an hour. (If you are on a sodium-restricted diet, check with your doctor first.)

Take an over-the-counter analgesic.

Use a hot-water bottle on stomach or back, mainly for psychic comfort.

More often than not, says Kilmartin, the offending E. coli and the attendant cystitis will flush right out of your system.

Kilmartin sees herself in the role of an elder woman in a village or on a street, back in the days when homely tips like hers were passed from woman to woman.

She's even sent a copy of her book to Lady Diana.

Two copies, in fact, "One for the bedroom library and one to take on trips. She's only 19, that girl, and she's going to have an awful lot of troubles. Why should she have bedroom problems added on top of that?