The Obama administration brief noted that California extends all of the rights and responsibilities of marriage to gay and lesbians, but forbids them the designation of "marriage."
That circumstance "particularly undermines the justifications for Proposition 8," Verrilli wrote.
"The brief pays closest attention to California and the other seven states that grant same-sex couples all the rights and responsibilities of marriage but insist on denying them the favored name," said Jane S. Schacter, a professor at Stanford Law School. "But it advocates that the court adopt a much tougher, more skeptical approach to any state law that denies same-sex couples the right to marry.
"That approach is what lawyers call 'heightened scrutiny,'" she added, "and if it were faithfully applied to all state laws banning same-sex marriage, it would result in the invalidation of those laws. The administration's brief provides a blueprint for a national right-to-marriage equality, even though it does not advocate that in express terms."
Stephen I. Vladeck, a professor of law at American University of Law, called it the "tip of a much larger anti-discrimination iceberg."
According the brief, Vladeck said, "states can't discriminate against gays without a really strong reason -- not just with respect to marriage, but adoption, employment, benefits and so on."
Today, 39 states have laws restricting marriage to opposite-sex couples. This number includes voter-approved constitutional amendments in 30 states barring same sex marriage. Nine states allow gay marriage.
"The brief filed by the solicitor general is a powerful statement that Proposition 8 cannot be squared with the principles of equality upon which this nation was founded," said Adam Umhoefer executive director of the American Foundation for Equal Rights (AFER), the group behind the challenge of Prop 8.