Macklemore & Ryan Lewis are one of the hottest acts on pop radio these days, having scored No. 1 hits with the lighthearted novelty song “Thrift Shop” and its bouncy follow-up “Can’t Hold Us.”

That is no small feat for a rap duo from Seattle without a major-label contract, but their single “Same Love” has the potential to be groundbreaking in a different way: it is the first song to explicitly embrace and promote gay marriage that has made it into the Top 40, gay-rights advocates and radio executives said.

“The fact that a song solely dedicated to the message of marriage equality is climbing the charts and quickly becoming a popular song across the country is a big deal,” said Charlie Joughin, a spokesman for the Human Rights Campaign, the largest gay rights organization. “It’s indicative of a changing attitude.”

Radio programmers say “Same Love” seems to have captured the nation’s mood, reflecting growing support among young adults for gay marriage in polling. It also hit the charts in February, just as several states began taking up the issue and the Supreme Court was considering challenges to the federal Defense of Marriage Act and to California’s ban on same-sex marriage.

On Wednesday, the same day the Supreme Court handed historic victories to same-sex couples in both cases, “Same Love” rose to No. 28 on the Billboard Hot 100 chart, up from No. 65 three weeks ago. On the strength of online streaming more than airplay, the song was No. 5 on the Rap Songs chart, where lyrics in support of gay rights are almost unheard-of. Sales of the single surged 23 percent last week from the previous week to a total of more than 788,000 copies, and views of the single’s video on YouTube had approached 53 million by Sunday.

Several radio programmers say surveys of listeners predict the song will continue to rise. “It’s been phenomenal,” said Tom Poleman, the president for national programming at Clear Channel Media and Entertainment, which operates 850 stations. “Everything we are seeing shows it’s going to be another monster hit for them.”

Support for gay rights is certainly not a new phenomenon in pop music. Frank Ocean, a singer in the hip-hop collective Odd Future, broke down barriers in R&B last year when he released “Channel Orange,” an album with songs about his love for a man. Lady Gaga’s “Born This Way” was a chart-topping song in 2011 that generally affirmed acceptance of homosexuality, and artists like Katy Perry, Fun and Kacey Musgraves have made support for gay rights part of their public personas.