MANCHESTER, N.H. (AP) — Sam Brownback, a Kansas conservative and favorite of evangelical Christians, will endorse his former Republican presidential rival John McCain, an advisory from McCain's campaign said Wednesday.

The nod could provide a much-needed boost, particularly in Iowa, for the Arizona senator and one-time presumed GOP front-runner whose bid faltered and who now is looking for a comeback.

Brownback will announce his support for McCain later Wednesday in Dubuque, Iowa, and then travel with the candidate to campaign in two other cities in the state, the McCain campaign advisory said.

It's uncertain how much weight the Brownback's backing will carry; the Kansas senator dropped out of the race last month with little money and little support. While he is a favorite of religious conservatives, he failed to persuade them to embrace him as the GOP's consensus conservative candidate. He spent months emphasizing his rock-solid opposition to abortion, gay marriage and other issues important to the party's right flank, but left the race ranking low in national polls and state surveys.

Still, Brownback's backing could signal to evangelical Christians that they can trust McCain and could help solidify McCain's credentials on social issues. The endorsement could be especially important in Iowa, where McCain trails in polls.

Despite a solidly conservative Senate voting record on social issues, McCain has a rocky history with cultural and religious conservatives who make up a significant part of the Republican base — and have proven to be influential in Iowa's GOP caucuses.

He once likened their leaders to ''agents of intolerance,'' but since has taken steps to heal his relationship with the voting group. Still, some are skeptical that McCain will be a loyal Republican who will champion their issues, partly because while his record is clear cut, he's not a high-profile crusader against abortion rights and gay marriage.