In the last seven years 31-year-old Jay G. Rainey, married, father of two children, has worked hard enough at his job with a manufacturing firm in Broadway, Va., to be named head of the plant's employee relations.

But today Rainey, along with two other Washington area men with apparently typical middle-class credentials, must give all that up: All three are to begin serving jail sentences for their part in a student antiwar demonstration that occurred on a Virginia campus seven years ago.

"It's a hell of a reason to send three people to jail who've build up their lives in the past seven years," said Rainey yesterday as he packed for his six-month stay in the Rockingham County jail.

Rainey will enter the jail with James W. McClung, 36, of Washington, and Stephen B. Rochelle, 29, of Fairfax. All were convicted of trespassing stemming from their participation in the demonstration at Madison College in Harrisonburg. Va.

The men's unsuccessful seven-year effort to have their conviction overturned by higher state and federal courts came to an end Friday when they were ordered by Rockingham Circuit Court Judge Joshua Robinson to report to the jail today.

According to Rainey, Judge Robinson acknowledged Friday that the three men were upstanding citizens and that the usual reasons for incarceration - punishment, retribution, rehabilitation - did not apply in their cases.

But Robinson said that in order to uphold the integrity of the judical process and the jury-sentencing procedure, he would not overturn the jury-imposed sentence.

In 1970, Rainey and Rochelle, who now is a survey computer with a Maryland engineering firm, were students and McClung a public information specialist at the Library of Congress, was an assistant professor of English at Madison. All three participated in a sit-in, along with about 40 students, at the school's administration building.

According to McClung, the demonstration was in protest to the war in Vietnam, alleged violations of student rights, and the school administration's alleged failure to renew contracts of some professors, one of whom was McClung.

The college administration called in police to dislodge the demonstrators, McClung said. Twenty-eight were later convicted in Harrisonburg municipal court of trespassing and each was given a $100 fine.

While they did not dispute the facts of the case. Rainey, Rochelle, McClung and four others argued that their constitutional right to free speech had been violated. In order to begin the appeal process, they asked for a trial in circuit court. In addition, they attempted to waive their right to a jury, according to their lawyer, John C. Lowe.

Rockingham Circuit Court Judge Hamilton Haas, as was his prerogative, denied their request. The circuit court jury that subsequently heard the case imposed six-month jail terms and $500 fines on both Rochelle and Rainey. Lowe said McClung received a nine-month jail sentence and a $1,000 fine. The four others were fined $500 each.

Over the past seven years the three men appealed to higher courts, U.S. District Judge Robert R. Merhige ruled that their right to free speech had been violated and that the college's rules governing demonstrations were too vague and broad. But Merhige's ruling was overturned by the 4th U.S. Circuit Court of Appeals. That court held that the first amendment rights of students on campus were not as broad as those of a citizen in public places, Lowe said.

Lowe said yesterday that he thought his clients were "getting punished vindictively for exercising their rights under the law to appeal." He said the same commonwealth's attorney, Jack Depoy, who recommended $100 fines in municipal court for the original 28 defendents, subsequently called the trespassing charge a "serious criminal offense" in front of the Rockingham circuit jury.

Depoy said yesterday he did not recalled making that statement and added, "I felt very strongly at that time they should have gone to jail. They're the ones who brought about the time delay. I don't see where the time delay changes anything."

Rochelle who "hoped" he would not lose his job during his time in jail, said, "I think it's an outrage . . . Criminals should be in jail, not people who are trying to exercise their constitutional rights. I'm very disppointed."

Would he do it again, McClung was asked.

"I think not. My principles have not changed. I still believe in the constitutional right of people who want to protest. But I would certainly not (do it again) knowing that the law's punishment was anything like what was meted out."