Joanne Joiner knows the advantage of taking 20 minutes a month to perform a task most women find frightening, frustrating, distasteful or too time-consuming.

In one of her monthly breast self-exams five years ago, she found a tiny lump in one breast. Unlike the fibrous lumps normal for the many women who have fibrocystic breasts like Joiner, this one was smaller and firmer. And it didn't go away.A couple of mammograms revealed little. A cancer specialist removed the lump and small amounts of tissue surrounding it and found a tiny, malignant tumor. A couple of armpit lymph nodes also contained cancer cells, so chemotherapy and radiation were administered to wipe out any cancer that had escaped the surgeon's knife.

Joiner, 60, talks nonchalantly about all this today, as if conquering breast cancer was as routine as getting married and having three kids. As Orlando-area coordinator for Reach to Recovery, the American Cancer Society's support organization for breast cancer patients, she has told her story many times.

But five years after surgery, with a clean bill of health, Joiner is still emphatic on this point:

"BSE (breast self-examination) does it!

"I still do it," she added. "I do it every month."

The facts on breast cancer in America are terrifying: It will strike one in 10 women in their lifetimes. There will be about 130,000 new cases this year, and more than 41,000 deaths.

The facts are also comforting: With early detection and treatment, the five-year survival rate for women with localized breast cancer has risen to more than 90 percent (up from 78 percent in the 1940s). Eight out of 10 breast lumps are benign. And refinements in surgery have made the removal of breast tumors far less mutilating than they were even a decade ago.

Many women who rely on doctors to examine their breasts are surprised to learn that the majority - 75 to 90 percent - of breast lumps are discovered by women themselves.

That makes it clear that women - not doctors or mammograms, though both are important - are the first line of defense against breast cancer. And the reason for monthly self-examinations is equally clear: The earlier a cancerous tumor is found, the lower the likelihood that the cancer has spread to surrounding tissue. If the cancer has not spread, options for treatment are greater and chances of full recovery are excellent.

Yet only about a third of American women say they regularly examine their breasts, according to a 1983 Gallup poll commissioned by The American Institute for Cancer Research. The reasons they neglect to are legion.

"I absolutely forget," said a 36-year-old Orlando professional woman. "Then I will read something about Ann Jillian or Sandra Day O'Connor's surgery, and that will remind me." Both the actress and the Supreme Court justice had surgery for breast cancer.

"I look for disfiguration or discharge, but as far as taking time to do the actual examination - I just don't do it," said another Orlando woman, 34, who said she should know better.

"When I didn't do BSE, the biggest reason was fear of finding something," said a 27-year-old Orlando social worker who works on a hospital oncology unit. "In the hospital, I see for the most part the worst cases."

But she persuaded herself to do breast self-exams at least sporadically three years ago and last year found a lump that turned out to be benign. Since then, she has done self-exams monthly.

"First I didn't do it out of fear. Now, I do it out of fear."

Women's health specialists say these women's reasons for not examining their breasts are typical.

"There are three predominant things I hear," said Nancy Christiansen, clinical coordinator at Florida Hospital Orlando's Center for Women's Medicine. Women "say they have such lumpy breasts they can't tell when there's anything unusual. Or they say if they don't check they won't find anything and be frightened. The other excuse is the universal one - time."

Other health professionals cite variations on those themes. Cathy Grenier, community education coordinator and oncology nurse at Orlando Regional Medical Center, adds another excuse she hears from older women: "For a lot of women over 50 or 60, it's not in their cultural background to feel comfortable touching their breasts."

The reluctance women have to examine their breasts is understandable, health experts say. Public education efforts have convinced most women that they should examine their breasts but have not taught them how. What women feel when they attempt self-examination is mysterious and unfamiliar - and the thought that any irregularity is potentially fatal makes it scary, as well.

Behavior analyst Hester Bloom was among a University of Florida team that developed a patented technique for breast self-examination called MammaCare, which she now teaches through clinics and doctors' offices in Sarasota.

Bloom said complaints from women that they don't know what to look for, how to look for it, and how to determine when they've found something significant "point to the need for some very comprehensive skills training." By using one-on-one instruction, films and breast models that simulate real breast tissue containing different kinds of lumps, the MammaCare method aims to provide that training.

UF psychology professor Henry Pennypacker, one of MammaCare's developers, said the way to overcome women's reluctance is "to teach them to be good at it." A yearlong follow-up on women who had learned the technique at a New York clinic showed that 85 percent were performing the method monthly.

Not everyone agrees that MammaCare, which costs about $50 to learn, is any better than the standard, American Cancer Society method. But it is widely acknowledged that adequate instruction is the missing link in getting women to feel confident enough to carry out monthly breast self-exams.

"Women get very exasperated - they can't tell what they're feeling and they wonder if the doctor will laugh at them," said Grenier, the ORMC community education coordinator. ORMC teaches the American Cancer Society method of breast examination in free classes, and the Cancer Society offers free seminars.

Given compelling evidence that early breast cancer detection saves lives and breasts, women must stop making excuses.

*Here are some sources for further information on the methods:

AMERICAN CANCER SOCIETY METHOD:

-Free package of information, or request speaker for group or club: local American Cancer Society chapter.

-Free brochure and hang-in shower reminder card: Orlando Regional Medical Center, Orlando, Fla., (407) 841-4636.

-Free informational packet. Send self-addressed envelope with 45 cents postage: American Institute for Cancer Research, Dept. BSE11, Washington, D.C. 20069.