WASHINGTON (Reuters) - Texas Governor Rick Perry, who dropped out of the Republican presidential race in January and initially threw his support to Newt Gingrich, endorsed presumptive nominee Mitt Romney on Wednesday.

Perry's endorsement was another sign of conservatives coalescing around Romney, who has been more moderate than some of his rivals for the Republican nomination.

Perry said the former Massachusetts governor, who sharpened his conservative rhetoric as the primary campaign wore on, had earned the nomination through hard work, a strong organization and a disciplined message.

"So today I join the many conservative Republicans across the nation in endorsing Mitt Romney for president and pledge to him, my constituents and the Republican Party that I will continue to work hard to help defeat President (Barack) Obama," Perry said.

Romney said on Twitter it was great to have Perry's support and he looked forward to working with him.

Gingrich, a former House of Representatives speaker who has campaigned as a conservative alternative to Romney, is dropping out of the race after Romney handily won primary victories on Tuesday that allowed him to claim the unofficial mantle of Republican nominee.

Conservative former U.S. Senator Rick Santorum ended his campaign earlier this month.

(Reporting By John Crawley; Additional reporting by Steve Holland; Editing by Peter Cooney)