PITTSBURGH (AP) _ A 77-year-old woman who claims her one-year jail term for simple assault was illegally converted into 20 years in a mental institution has a court appointment with a doctor she accuses of violating her rights.

In a case scheduled for jury selection today before U.S. District Judge Paul Simmons, Ella Hornick alleges that Dr. Anthony Moats, now retired, libeled her and violated her civil rights in statements he made about the reasons she was in Mayview State Hospital outside Pittsburgh.

Miss Hornick, acting as her own attorney, is also pressing legal actions against other doctors, lawyers and a judge, Samuel Strauss of Allegheny County.

Shiela Ford, a deputy attorney general defending Moats, declined comment Monday on the woman's claim against Moats.

Miss Hornick says she is arguing her own case because private attorneys have either refused to take her case or required large advance fees that she can't afford. She says her monthly income is about $420 in Social Security benefits.

The commonwealth was released as a defendant from the Moats case because it is immune from such actions, and 10 other individuals were released because a two-year statute of limitations had expired on her claims.

Miss Hornick claims her 1952 sanity hearing was improper and she was unjustly committed against her will until a further court order, which did not come until 1974.

Miss Hornick was committed after Strauss, then an assistant district attorney, won a conviction of simple assault and battery against her in 1952 for discharging a tear gas pen at two neighborhood youths. She says the youths were harassing her in a dispute over her home, which her estranged husband sold to a neighbor while she lived there with her son.

''By no stretch of the imagination could this have happened to a man. The judge would have said 'Thirty days,' and thrown him in the hoosegow,'' said Dr. Colter Rule, a New York psychiatrist who offered testimony in Miss Hornick's behalf after reviewing her records.

A doctor who first examined her at Mayview wrote that Miss Hornick, then 44, was ''neat ... her speech is well organized, she has very good English ... both insight and judgment are intact.'' But the doctor recommended keeping her there for a ''paranoid condition'' that likely could not be cured.

''Paranoid condition, that could mean a paranoid character, a personality trend. That's not psychosis. We've got plenty of lawyers and judges on the bench who have paranoid character structures,'' Rule said in a recent phone interview.

In Miss Hornick's discharge notes, however, Moats allegedly wrote that she had been diagnosed paranoid schizophrenic, a major mental disorder characterized by separation of the thought processes and emotions.

''On the basis of the records, there's no data to substantiate a diagnosis of paranoid schizophrenia,'' Rule said. ''She may be a contentious, argumentative lady, but that's not the same.''

The state Supreme Court ruled in 1955 that personality disorders are insufficient to justify involuntary committals, Miss Hornick said.

''Why would they hold her for 20 years? It was really patently absurd,'' Rule said.

Miss Hornick alleges that other irregularities in her case include the disappearance of Mayview's records about her from 1952 to 1957, conflicting court records about her sanity hearing and a forged signature on a document related to her bid to overturn her conviction.

Miss Hornick, who audited college law courses in Wisconsin after her release, said she will try to reinstate her federal case against the individuals who were released. She cites a legal theory that ''fraud upon the court'' delayed the tolling of the statute of limitations.

''There are lots of procedures I could try,'' she said. ''A lot of attorneys won't try them because they're complicated and take a lot of time. I've got some time left.''