ATLANTA — Cumulus Media Inc. is buying Citadel Broadcasting Corp. in a $1.7 billion deal that would unite two of the nation’s largest radio station owners.

Atlanta-based Cumulus would own 572 radio stations across about 120 U.S. markets once the deal announced today closes. It will remain the No. 2 radio station owner in the U.S. behind Clear Channel, which owns more than 800 stations.

Citadel owns four stations in the Portland FM radio market: WBLM, WCYY, WHOM and WJBQ.

The deal represents a bet that the radio advertising market will continue rebounding. Like other media, radio broadcasters were hard hit in 2008 and 2009 as the recession curtailed the ad spending that generates most of their revenue. An advertising shift to the Internet also siphoned money away from radio stations.

But the outlook has been improving modestly as the recovering economy has encouraged advertisers to increase their marketing budgets.

Cumulus said today it is paying $37 per share in cash and stock for Citadel, which owns 225 radio stations in more than 50 markets. Las Vegas-based Citadel had previously rejected a $31 a share offer from Cumulus.

The deal must still be approved by Citadel shareholders and regulators. It is expected to close by the end of this year.