Kirk Johnson / New York Times News Service

MOSCOW, Idaho — The border with Washington state is just two miles from the home that Henry Johnston and Alex Irwin own here in western Idaho, but for a gay couple it might as well be a thousand.

Over there, just a brisk morning’s walk away, same-sex marriage was approved by a majority of statewide voters last fall; over here, the Idaho Constitution, through an amendment passed by voters in 2006, says that even a civil union granted elsewhere has no validity.

“Set your clock back,” Johnston said of his daily commute home from a job in Pullman, Wash.

The nation’s patchwork geography of same-sex marriage laws was not much of an issue when just a few outlier states granted the privilege. But now nine states and the District of Columbia allow such unions, with Maine, Maryland and Washington voting to join the list last fall. And the U.S. Supreme Court could decide this summer whether equal marriage protections are a right under the U.S. Constitution.

On Thursday — the last day it could — the Obama administration expressed its support for the case seeking to overturn California’s Proposition 8 ban on gay marriage, which the high court will hear this month. Its brief says gay and lesbian couples there have the same “equal protection” rights to wed, and that voters in the state were wrong to ban it. The administration brief urges the court to take a skeptical view of similar bans and contends that denying gays and lesbians the right to marry violates the Constitution’s Equal Protection Clause, though it does not explicitly call for gay marriage rights across the U.S.

On Monday, a group of prominent Republicans got there first, signing a brief to the court addressing the second gay marriage case, against the federal Defense of Marriage Act that limits marriage to one man and one woman. The Republicans argue that marriage is a constitutionally guaranteed right.

All that has made the borders, and the sharp disparities between states, more important and complex than ever for gay couples, and for interstate tourism as well. The marriage license office in Clark County, Wash., across the Columbia River from Portland, had to increase its hours to serve border couples when Washington’s new law took effect.

The Episcopal Church said last month that the National Cathedral in D.C. would soon begin conducting same-sex marriages. But if newlyweds drive home to the city’s suburbs in Virginia, any rights granted under the vaulted limestone arches will disappear under Virginia’s constitution.

Johnston and Irwin, both proudly gay and proudly Idahoan, said they had thought about taking a Sunday drive to get married and then dismissed the idea out of hand. Marrying across the border and returning home to a place where none of it had legal meaning, they said, or picking up and moving to Washington to obtain marriage protections would represent equal measures of surrender and defeat. For them, the battle for rights and recognition is to be waged at home, in a deeply conservative state where same-sex marriage remains, for now, an unlikely dream.

“How are things going to change if people aren’t there to help make them change?” said Irwin, 25, who grew up mostly in Pullman, home of Washington State University.

Johnston, 27, was born and raised in an Idaho timber-cutting town. He rejected the idea of marrying just to make a statement. “The minute we drive across the border it would become invalid and we’d be back to just being two guys who own a house together,” he said in an email.

The message is clear, Johnston added in an interview, that they are staying put to fight. “We’re not going anywhere,” he said.

Hardly anyone imagines that Idaho and conservative places like it — voters in 30 states, including Oregon, have banned same-sex marriage by statute or constitutional amendment — are likely to be moved anytime soon to a full embrace of gay life. The portrait, or caricature, of the American West in films like “Brokeback Mountain” has not entirely faded.

Even adding protections for gay men and lesbians to Idaho’s Human Rights Act has hit a wall, with advocates unable to get the Republican-controlled Legislature to print a bill, let alone hold a public hearing, after years of trying.

But on the local level, the picture is changing, slowly, and it depends on where couples live.

In just the last two months, two Idaho cities, Ketchum and Boise, have passed nondiscrimination ordinances protecting gay, lesbian and transgender people in housing and employment. Three more communities, including Johnston and Irwin’s town, are debating it. Before December, only one place, the small town of Sandpoint in the state’s panhandle, had enacted such protections.

Changes beyond Idaho’s borders, including a subtle shift in policies in Utah by the Mormon church, which has a huge influence in Idaho, have given gay people here added resolve and have provided crucial political cover for their supporters. In late 2009, the Church of Jesus Christ of Latter-day Saints said it would support nondiscrimination protections for gays in Salt Lake City, home to the church’s headquarters. About one-fourth of Idaho’s population is Mormon, a higher percentage than any state besides Utah.

“I believe the support of the Mormon church is key,” John Reuter, a former Sandpoint City Council president, said of the town’s nondiscrimination statute. “That the LDS church supported it in Salt Lake had a ripple effect in Idaho.”

With more gay people, especially younger ones, living openly in their communities, the discussion has become less about a class of people than about individuals.

“Who gets the credit here is the lesbian and gay community, who have had the courage to come out,” said Mayor Randy Hall of Ketchum, a resort town near Sun Valley.

Other people said the personal and the political were melding. That President Barack Obama offered his support of same-sex marriage last year, and that majorities of voters in three states did the same, prompted a new discussion about Idaho’s path. To many younger people, though, what matters is down the block or in the school cafeteria, not across the border.

“I’ve listened to this national debate,” said Lauren McLean, a member of the Boise City Council and a co-sponsor of the city’s new nondiscrimination law. “But my kids aren’t influenced by a national debate,” she added. “They just say, ‘Discrimination isn’t OK.’”

Here in Moscow, Johnston and Irwin said they were comfortably open about their lives, even holding hands in public. Last month, Johnston started a two-hour radio show on a local community station called “Give My Regards to Broadway,” and on a recent Sunday he played his favorites from the Broadway hit “La Cage aux Folles.”

“It doesn’t get any gayer than that,” he said.

But Johnston’s message was severely limited in its reach by KRFP radio’s tiny 100-watt signal. However fervently expressed in words and music, the show can barely be heard beyond downtown.

Republicans who back a federal right to marry

More than a hundred Republicans have added their names to a legal brief urging the Supreme Court to declare that gay couples have a constitutional right to wed. The Democratic White House, too, has come in on the side of same-sex marriage — but at this point, the Republicans who signed the document are taking a more expansive stance than President Barack Obama, who favors gay marriage but has said generally he would leave it to the states.

Business interests sometimes aligned with the GOP have voiced a similar opinion. In a separate brief last week, some of the nation’s largest companies said the federal gay marriage ban imposes serious administrative and financial costs on their operations. That brief drew 278 signers, including more than 200 companies — among them giants like Citigroup, Apple, Mars and Alcoa — as well as city governments, law firms and other groups.

While such friend-of-the-court briefs are not legally binding, the filings could have some influence on the justices. The list of Republicans includes these notable names:

• Alex Castellanos, Republican adviser and media analyst

• Mary Cheney, Bush administration adviser and former Vice President Dick Cheney’s daughter

• David Frum, former aide to President George W. Bush

• Mark Gerson, conservative author

• Benjamin Ginsberg, lawyer for the Bush-Cheney campaigns

• Carlos Gutierrez, commerce secretary under Bush

• Stephen Hadley, national security adviser to Bush

• Richard Hanna, current congressman from New York

• Jon Huntsman, former Utah governor and presidential candidate

• Gary Johnson, former New Mexico governor and presidential candidate

• Ken Mehlman, former Republican National Committee chairman

• Beth Myers, senior aide to Mitt Romney and his 2008 campaign manager

• Michael Powell, former Federal Communications Commission chairman

• Ileana Ros-Lehtinen, Florida congresswoman and chairwoman of the House Committee on Foreign Affairs

• Steve Schmidt, senior strategist for John McCain’s 2008 campaign

• Jane Swift, former Massachusetts governor

• William Weld, former Massachusetts governor and assistant U.S. attorney general

• Christine Todd Whitman, former New Jersey governor and EPA chief

• Meg Whitman, 2010 GOP nominee for governor of California

Sources: New York Times, Politico, American Foundation for Equal Rights