The Supreme Court heard lawyers argue yesterday whether the penalties for pregnancy imposed by two employers violated civil rights laws forbidding sex discrimination.

One of the employers, Nashville Gas Co., as a matter of policy pays sick leaves to employees disabled by heart attack, auto accidents, back trouble and other afflications unrelated to their jobs. The Tennessee utility also credits them with across-the-board pay increases approved while they are away and lets their seniority build normally.

But when female employees take pregnancy leave, the firm, also as a matter of policy, puts them on leave without pay and strips them of their job seniority.

For Nora D. Satty, whose clerical job was eliminated by a computer after she had an unplanned pregnancy, these are the results:

She lost $732 in wages during the three months she was away to have a baby in early 1973.

Her 3 1/2 years of seniority were wiped out.

She was rehired for a temporary project, at a starting wage $10 under her previous pay of $142.80 a week.

She applied for three permanent jobs, any one of which would have been hers had she been on sick leave, but lost each to a woman with less seniority.

She was fired when the temporary project ended a month after it had started.

Justices Harry A. Blackmun and Thurgood Marshall asked for the company's justification for taking away seniority from women employees who leave to have a child.

Nashville Gas rewards employees whose personal values dictate that they stay on the job rather than putting their personal lives over their employer's interests, replied attorney Charles K. Wray.

Justice William J. Brennam Jr. inquired if the utility would give its usual sick-leave advantages to an employee injured in an auto accident caused by his or her own gross negligence.

Wray said that such an employee was owed the same presumption as a heart-attack victim: he'd rather be at work than in a hospital bed.

But in the case of a pregnant woman, the presumption is that she wants a child, he said. No one inquired about the possible relevance of the accidental nature of Satty's pregnancy.

Wray apparently astonished Marshall by citing a company "right" to return Satty to her job, giving her preference over an outsider.

"She also had a right to the job if no one in the world wanted it," Marshall remarked.

For Satty Robert W. Weismuller Jr. argued that the company had injured his client "forever," partly be sending her to the bottom of the seniority and pay scales, without demonstrating such actions to be business necessities.

Wray, however, said the company merely had followed a "straightforward pregnancy policy" that was not a subterfuge to evade the Civil Rights Act of 1964, and that was consistent with a Supreme Court decision in a case involving General Electric Co., last December.

The justice devoted a second hour to arguments involving Sonja Lee Berg, a Richmond, Calif., kindergarten teacher. She was the sole bread-winner for her husband, who was studying for the ministry, and herself.

After she became pregnant five years ago, she sought to continue teaching right up to the onset of childbirth. Her personal physician certified that she could do this.

But the Richmond Unified School District insisted she comply with a policy requirement to take maternity leave, without drawing on her accrued sick leave pay, starting the first day of the seventh month of pregnancy. The school board also ordered her to submit to an examination by a board physician. She refused, and won a court injunction allowing her to work until just before the baby's birth.

Berg's attorney, Mary C. Dunlap, argued yesterday that the board never showed distrust of a non-pregnant employee by ordering an examination by its own doctor. In contrast, school board attorney Arthur W. Walenta Jr. said school authorities had a right to seek medical information about Berg through the board's own physician.

The Ninth U.S. Circuit Court of Appeals ruled for Berg, saying she was entitled to both the sick and legal fees, and ordered the school board to grant similar benefit's in similar cases.

In like fashion, the Sixth U.S. Circuit Court of Appeals, ruled that Nashville Gas owed Satty sick leave pay, $9,456 in gross wages she otherwise would have earned reinstatement with full seniority, and attorney's fees.

Arguing for overruling the appellate courts, lawyers for both employers cited the GE decision, which involved a sickness and accident plan providing benefits without regard to sex, but excluding benefits arising from pregnancy.

A divided court held that the plan did not violate the Civil Rights Act, saying that gender-based discrimination does not result simply because disability benefits are not all-inclusive.