The Supreme Court agreed yesterday to review two decisions extending the constitutional guarantee of due process of law to students facing expulsion or suspension.

One case affects graduate and professional schools. It developed four years ago when the University of Missouri School of Medicine at Kansas City expelled Charlotte M. Horowitz, of the District of Columbia, just as she was about to graduate.

The second case comes from Chicago, where public school officials suspended one pupil for violating a rule against wearing an earring and another for violating a rule against smoking marijuana.

Appelate courts ruled that hearings should have been held in both cases, that Horowitz also was entitled to have the charges against her spelled out, and that the two suspended chicago students were entitled to unspecified damages.

Horowitz had superb - and undisputed - academic qualifications. In the Medical College Admissions Test she ranked in the top 1 per cent. In 1973, the year in which she was to graduate, she scored first in her class in an exam given by the National Board of Medical Examiners.

The reasons given for her explusion were unrelated: all allegations that she could not get along with patients, faculty members and classmates, and that her personal hygiene - such as occasionally dirty fingernails and laboratory coats - was poor.

Horowitz disputes such allegations, saying she was victimized by sex discrimination and anti-Semitism. Specifically, for example, she said "My lab coats were washed every week, even if they weren't the whitest."

Court papers show that by the summer of 1972, several faculty members were on record as being disturbed by her hygiene and rapport with others. "She did not exemplify what they were looking for in terms of personal appearance," one staff member has testified.

In a letter in February, 1973, school administrators notified Horowitz that she "must make very marked and substantial improvements in . . . clinical competence, peer and patient relationships, personal hygiene and ability to accept critism." But she noted she received a superior or satisfactory rating in eight of nine categories of clinical competence.

The school asked a panel of seven of its physicians - none of whom had previous contact with Horowitz - to evaluate her case. Two recommended that she be allowed to traduate on schedule in the spring of 1973, two that she could remain in school, but on probation, and two that she be expelled. Two faculty committees that screened the recommendations concluded she could be dismissed. She was, in July, 1973, without a hearing.

Horowitz sued but lost in U.S. District Court. The judge specifically found no evidence to support her contention that she was a victim of sex discrimination and anti-Semitism.

The Eigth U.S. Circuit Court of Appeals, however, ruled for her. "The unrefuted evidence . . . established that Horowitz has been stigmatized by her dismissal in such a way that she will be unable to continue her medical education, and her chances of returning to employment in a medical related field are severely damaged," the court said. "The dismissal was effected without the hearing required by the 14th Amendment," which forbids deprivation of liberty without due process.

Horowitz has been unemployed and supoorted by her family since the expulsion. She had been promised - but never got - a job at the University of North Carolina Medical School on the condition that she hold a medical degree.

In the Chicago case, fifth-grader Siles Brisco wore an earing. He said this symbolized black pride; the authorities said they believed it denoted membership in a gang. Finally, they suspended him for 20 days - without a factual hearing on the meaning of the earring.

The other pupil, Jerius Piphus, was accused of, but denied, smoking marijuana. School officials covened a hearing, but excluded legal aid lawyers who tried to tape it.He was give a 20-day suspension, later cut to five days.

A federal judge ruled the suspensions unconstitutional but denied damages. The Seventh U.S. Circuit Court of Appeals ordered the case sent back so that relief and damages - "neither so small as to trivialize the right nor so large as to provide a windfall" - could be granted. At most, say Chicago school officials, damages should be $1.