Patty Moscoso, who moved to Rockville from Peru two years ago, has made friends easily at Peary High School where she is a junior. But she always waits until she's known someone awhile before she breaks the news about her 11-year-old brother Luis.

"Most of them don't mind when I finally tell him about him, but some of my friends, when they found out, never speak to me again," she said.

Patty's brother is autistic, a disorder that is widely misunderstood and frightens many people.

Recently, for the first time in her life, Moscoso found a group of people who cared and understood about autism when she went to a gathering held by the Maryland Society for Autistic Adults and Children (MSAAC).

The society, formed in 1971, is one of the most successful state branches of the Washington-based National Society for Autistic Children which has 49 state organizations comprising 160 local chapters and 6,000 members. Only Wyoming has no organization.

The Maryland unit "is one of a few in the country that actually takes autistic adults who have lived in institutions most of their lives and helps them to live and work in a normal community environment," said Pat Juhrs, executive director of MSAAC.

Two years ago MSAAC set up a residential program that now houses nine autistic adults in three Montgomery County apartments staffed with live-in counselors.A second program, started last September, provides vocational training for the nine residents. By the end of the year three more autisitc adults will join the vocational program.

The entire program, with an annual budget of $200,000 provided by the Maryland Department of Health and Mental Hygiene, employs 12 full-time and two part-time staff members.

"Thirty years ago 95 percent of all autistic children were institutionalized by the time they reached puberty," said Jane Salzano, president of MSAAC, whose 23-year-old son Brian is in the residential program.

The difficulty of slowly teaching autistic people to live in an apartment, take out the trash, do the laundry, go to a job each day or maintain a checking account cannot be appreciated without understanding the disorder.

Autism was first discovered in 1943 by Dr. Leo Kanner, of Johns Hopkins University, who died two weeks ago. Although scientists now know that it is a severe neurological disorder, it was not until last fall that the U.S. Office of Special Education removed autism from the category of "severely emotionally disturbed." For many years the condition was thought to be a psychological disorder most often caused by cold, indefferent parents.

An expert on autism, George Francis Warren Jr., has pointed out that "the brains of persons with autism function differently. People with this disability do not understand what they see, hear or sense in the usual manner. Thus, autism causes severe learning, communication and behavior problems.

"Subtle brain damage at or prior to birth . . . produces autism. Nothing in the psychological environment of a child has proven to cause (autism). Parents, above all, are not to be blamed," wrote Johnson, acting executive director of the National Society for Austistic Children.

More than half of the autistic population (approximately 300,000 in the United States) has severe behavioral disorders. Autistic children have been known to beat their heads against walls for hours, throw themselves down steps and stare off into space for long periods of time. Many respond only rarely to people around them, but at other times their behavior can be highly erratic.

However, autism has different degrees of severity and it is only those most seriously afflicted that suffer from these severe behavior disorders. One of the sympthoms of autism that distinguishes it from mental retardation is the ability of autistic people to improve dramatically, many to the point where it is hard to tell they are autistic.

For example, one autistic young man lives by himself and works in Montgomery County. His only overt symptom is slow speech.

Although about half of all autistic people are mute and/or have low IQs, some show near-genius abilities in specific areas such as art, math, music and memory which are functions of the nondominant region of the brain.

The mother of an autistic child read the alphabet to her young son and, after hearing it once, he was able to recite it backward and forward in rapid succession.

Another autistic girl began showing near-genius talent in music at the age of 19 months, when she sang rhythmic songs using perfect pitch. By the time she was 4, she could play sonatas and melodies after hearing her mother practice them, and once played an entire book of songs without a mistake.

Sam Dashner, 22, who has been in MSAAC's residential program for two years can tell you what day of the week almost any date falls on.

"Sam, what day was May 23, 1958?" asked Rene Thirion, a house counselor who lives with three autistic men at MSAAC's Glenmount Park apartment in Wheaton.

"Thursday," replied Dashner immediately.

Echolalia, or responding to a statement by simply echoing the last few words, is also evident in many autistic people.

Kenny Stein, 23, who lives with Thirion, is a good example of someone with the speech patterns of echolalia.

"I have a nickname for him -- Radar," laughs Thirion.

"He's gotten to the point that he repeats what I'm going to say even before I say it. Like I'll get ready to tell him to take out the trash and Kenny will look at me and say 'Take out the trash' before I say it. It's really amazing," said Thirion.

Although the exact cause of the neurological disorder is not yet known, research indicates autism may be caused by certain chemical agents to which a child's parents have been exposed. Scientists also believe it may result from metabolic, infectious, genetic or other disease activity, including perinatal cardiorespiratory distress, causing a type of brain damage that occurs before, during or shortly after birth.

While the means to prevent or cure autism remain unknown, victims of the disorder can make remarkable improvement through therapy and programs such as those established by MSAAC.

Another program proposed by the Maryland organization that would aid severely autistic adolescents was given $50,000 by the Maryland Developmental Disabilities Council last month.

"We hope to set up a special education program within a Montgomery County high school so there is interaction with other teen-agers," said Juhrs.

"Three teens initially will be admitted to the program and live in homes near the school," she said. "Currently there is no education program for autistic teen-agers. Most of them are sent out of state, some as far away as Florida and Connecticut. When the program is fully operating, hopefully by May 30, it will be the only one of its kind in Maryland."

Indeed, MSAAC is one of the few organizatios that places so much emphasis on bringing autistic adults out of insitutions to help them become part of a community. Even MSAAC's parent organization, the National Society for Austistic Children, lends its name and much of its efforts to children and not to the difficult adults.

"As our generation of (autistic) children was growing up, we realized that there would be no services for them when they grew up. So we took the bull by the horns and started these services," explains Salzano.

However, Jeanne Simons, who in 1954 founded Linwood Children's Center in Ellicott City, which serves autistic children, and has run it for 27 years, sums up a still common attitude toward autistic adults.

"The (autistic) children are like kittens and when kittens grow up, they're cats," says Simons. "Everyone likes little kittens because they're cute, but when they become cats, not everyone wants them anymore."