In a closely watched case, Deputy Attorney General Jared Maag said legislators have such broad latitude in setting policy that "any conceivable, rational basis" would justify the different treatment.
Maag argued in favor of upholding a sentence of more than 17 years in prison for Matthew R. Limon, convicted of criminal sodomy for having sex at age 18 with a 14-year-old boy in 2000.
Had the victim been a girl, Limon could have been sentenced to one year and three months in prison under a 1999 "Romeo and Juliet" law that gives shorter sentences to heterosexuals if the partners' ages are within four years and under 19.
His attorneys argued the different treatment represents discrimination against gays and lesbians and is unconstitutional.
But Maag said the different treatment is acceptable if legislators can argue there's a rational reason -- including promoting traditional values.
"If you admit there's a conceivable basis that's at least arguable, then that is enough to uphold the statute as constitutional," he said.
James Esseks, an American Civil Liberties Union attorney representing Limon, said the state has "fanciful justifications" for the harsher sentence.
Esseks said the state is basing its law on "private prejudice," which is constitutionally unacceptable.
