Can a state punish a man but not a woman for having sex with a juvenile who consents to it? Can a state compel a man but not a woman to pay alimony?

Both questions are before the Supreme Court in cases involving the guarantee in the Constitution of the equal protection of the laws.

One case grew out of a conviction for so-called statutory rape, in which the victim traditionally has been defined by law always to be female and never to be male.

The case comes from New Hampshire, which, over the course of more than a century, has varied the age under which a female becomes a victim from 10 to 13 to 16 to 15 and, finally, back to 13.

In 1973, when the law made it a felony for a male to achieve "any penetration, however slight," of an under-15 female, Thomas E. Meloon, then 24, and divorced, had sex three times with a 14-year-old girl, with her consent.

A year later, Meloon was convicted and sentenced to seven to 15 years in prison. After serving 3 1/2 years, however, he was released on bail in 1977 because the 1st U.S. Circuit Court of Appeals struck down the law as unconstitutional.

The state gave four arguments for its contention that the law did not deny equal protection:

Some under-15 males are physiologically incapable of becoming victims of consenting sex, making males as a class less vulnerable than females as a class to offenders.

Some men have a disorder that erotically attracts them to children, making men as a whole more likely than women as a whole to commit the offense.

Injury is more likely to be suffered by girls than boys who engage in sex.

Males can't become pregnant.

Chief Judge Frank M. Coffin rejected all four claims, saying that the state had documented none and that "its very premises are open to question."

He found "no reason" to believe that the majority of pre-pubescent boys could not achieve "any penetration, however slight," and said that the evidence indicates that "the number of potential victims in the class of males under 15 may include the great majority of the class members."

As to a diseased craving for children, Coffin said the state had provided no evidence on its incidence among normal males, on the number of victims among men convicted of statutory rape, or on the possibility of neuroses that may induce women to seek out under-15 males.

The judge of course had no dispute with the point that only women become pregnant. But, he said the state offered "not an iota of testimony or evidence that the prevention of pregnancy was a purpose of its statutory rape law."

Moreover, Coffin said, the pregnancy rationale doesn't square either with the drastic changes the state has made in the age below which sex becomes an offense, or with other New Hampshire laws that deal with illegal sexual conduct, such as adultery, incest and prostitution, without regard to whether the offender is male or female.

He also pointed out that in August 1975, New Hampshire repealed the statutory rape law and replaced it with one that is gender-neutral and that sets the age of the victim, female or male, at under 16.

In a brief requesting Supreme Court review, the state generally repeated the arguments rejected by Coffin.

Meloon's lawyer, Eleanor Krasnow of Manchester, urged the court to affirm the 1st Circuit. Her arguments included these:

The girl had engaged in sex "willingly, even lying about her age in order not to discourage" him, had had "a number of prior sexual experiences," and was not shown to have suffered any harm from sex with Meloon.

The girl and Meloon, who "used no force," previously had "maintained a social relationship."

Of 41 jurisdictions she has checked, 21, including Maryland (but not the District of Columbia and Virginia) have replaced their old statutory-rape laws with gender-neutral ones.

In the alimony case, the Alabama Supreme Court upheld a ruling that William H. Orr was not denied equal protection by state laws that would not allow alimony to be awarded to a divorced husband.

Orr and his wife, Lillian, were divorced in February 1974. He signed an agreement to pay her $1,240 a month, pay off the $4,800 balance owed on her 1973 Chevrolet Corvette and give her their house in Auburn (although she would pay off the balance of the mortgage).

Orr also agreed to pay the premiums on $108,000 in life insurance policies that name her as the beneficiary, to pay her divorce lawyers' fees of $3,500, and to share equally with her any increase in his taxable income, which at the time was $26,000.

In August 1976, when Orr was $3,312 in arrears, he filed an unsuccessful motion to have the decree ruled illegal on equal-protection grounds. He now lives in Santa Clara, Calif., and his former wife in Opelika, Ala. They had no children.