WASHINGTON — The United States government on Friday urged the Supreme Court to strike down state bans on same-sex couples' marriages across the country, concluding, "There is no adequate justification for such a discriminatory and injurious exercise of state power."

The filing in the cases challenging bans in Kentucky, Michigan, Ohio, and Tennessee represented nearly the end of a long path for the Obama administration on the issue, which began with President Obama opposing marriage rights for same-sex couples and his administration defending the constitutionality of the Defense of Marriage Act.

In May 2012, though, Obama announced his support for same-sex couples' marriage rights — helping to change the national landscape on the issue in the months before voters in three states voted for marriage equality measures at the polls.

On Friday, the Justice Department — which stopped defending the constitutionality of DOMA in February 2011 — told the Supreme Court, "The marriage bans challenged in these cases impermissibly exclude lesbian and gay couples from the rights, responsibilities, and status of civil marriage. These facially discriminatory laws impose concrete harms on same-sex couples and send the inescapable message that same-sex couples and their children are second-class families, unworthy of the recognition and benefits that opposite-sex couples take for granted."

Showing how far the law has traveled in a few short years, the brief goes on, "The bans cannot be reconciled with the fundamental constitutional guarantee of 'equal protection of the laws.'"

Specifically, the administration noted, "The President and Attorney General have determined that classifications based on sexual orientation should be subject to heightened scrutiny." That decision, made when the administration shifted gears on DOMA in 2011, would — if adopted by the Supreme Court — mean that laws and governmental policies that classify people based on sexual orientation should be viewed by courts with additional skepticism.

For example, laws that classify people based on race only survive court review if they are narrowly tailored to advance a compelling governmental interest. Laws that classify based on sex, for the example most advocates expect also would be applied to sexual orientation claims, must be advance an important governmental interest in a way that is substantially related to that interest. Without any such heightened scrutiny, laws must only be rationally related to a legitimate government interest.

"Heightened scrutiny under the Equal Protection Clause is particularly appropriate in the context of legal barriers to marriage," the administration argued on Friday. "A State should be required to present an especially strong justification for a law that excludes a long-disadvantaged class of persons from an institution of such paramount personal, societal, and practical importance."

Because, the administration argues, none of the claimed reasons supporting the bans meet that heightened scrutiny, they should fail.

In 2013, when California's Proposition 8 was before the justices, the administration took a similar position — but offered the court a limited ruling that only would necessarily result in striking down marriage bans where the state otherwise offered same-sex couples all of the benefits of marriage — but not the name itself. That argument held little water during oral arguments, with Solicitor General Donald Verrilli Jr. facing tough question on the middle-ground position from both ideological sides of the bench.

This time, the administration placed no such limit on its argument, stating that all such bans are "incompatible with the Constitution."

It went even further than that, though, arguing that "heightened scrutiny" isn't even necessary for the court to strike down the bans because the "reasoning and result" of the Supreme Court's decision striking down DOMA in United States v. Windsor "strongly support the conclusion that the bans at issue here are likewise unconstitutional." The administration notes that the justice found DOMA unconstitutional after reviewing "that law with 'careful consideration."

Looking at the Supreme Court's history since the mid-1990s in cases addressing gay rights, the administration lawyers write, "The marriage bans at issue here, like the [Colorado] law invalidated [in 1996] in Romer v. Evans," should be fund to be unconstitutional because they "'impose[] a broad and undifferentiated disability' on lesbian and gay people with a 'sheer breadth ... so discontinuous with the reasons offered' that they violate equal protection."

In addition to the Obama administration's brief, more than 200 congressional Democrats, led by each chamber's Democratic leader, filed an amici curiae brief supporting a marriage equality ruling from the court.

Other briefs supporting marriage equality have been coming in over the course of the past week. The states' briefs defending the bans are due March 27, supportive amicus briefs due by the next Friday, and the oral arguments in the case are set for April 28.