By Andrew Gray

AMMAN, April 16 (Reuters) - U.S. Defense Secretary Robert Gates arrived in Jordan on Monday to begin a Middle East trip that will also include stops in Egypt and Israel.

Gates planned to thank U.S. ally Jordan for its support and discuss recent developments in the region, including Iran's detention of British sailors and marines, with King Abdullah, a senior U.S. defense official said.

"Jordan has always been a strong ally of the United States and I look forward to discussing with the king how we can contribute to his efforts and how Jordan can contribute to ours," Gates told reporters travelling with him.

He cited efforts to stabilize Jordan's neighbour Iraq, the situation in Lebanon and relations between Israel and the Palestinians as topics of mutual interest.

"The Jordanians have for a long time been a very constructive influence and I look forward to continuing that," Gates said.

The senior defense official, speaking on condition of anonymity, said Gates wanted to hear the king's analysis of Iran's recent actions.

"I think he's going to want to look and see what King Abdullah has to say about Iran - what exactly is the context of some of the Iranian activity...of late?" the defense official said.

Earlier this month, Iran released 15 British military personnel detained by its Revolutionary Guards in the Gulf in March.

U.S. officials are keen to reassure its Sunni Arab allies in the Middle East, anxious that Shi'ite-dominated Iran is gaining influence in the region, that Washington will stand by them.

Gates and other U.S. officials have repeatedly stated that they do not plan to attack Iran and want to resolve their differences diplomatically.

Washington accuses Iran of using its nuclear program to develop atomic weapons and has also said that Iranian agents are supplying weapons used to attack U.S. troops in Iraq.

Iran says its nuclear program is only for generating electricity and denies fuelling violence in Iraq.

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