WASHINGTON, Oct 5 (Reuters) - The US State Department said on Tuesday it had warned the Lebanese government about the risks of a visit by Iran's president to Lebanon next week.

Lebanese officials expect President Mahmoud Ahmadinejad of Iran, a staunch ally the Lebanese Shi'ite group Hezbollah which dominates southern Lebanon and which the United States views as a terrorist organization, to visit Beirut on Oct. 13-14.

Ahmadinejad's visit is his first to Lebanon as president and comes at a time of greater tension in Beirut in the run up to indictments expected to be issued against Hezbollah members in the 2005 assassination of statesman Rafik al-Hariri.

Lebanon's largest parliamentary bloc, the Western-backed March 14 coalition, voiced concern last week about the visit, saying Ahmedinejad regards Lebanon as an Iranian base on the Mediterranean.

U.S. Secretary of State Hillary Clinton raised the issue of Ahmadinejad's proposed visit when she met Lebanese President Michel Suleiman in New York last month on the sidelines of the U.N. General Assembly.

We expressed our concern about it given that Iran, through its association with groups like Hezbollah, is actively undermining Lebanon's sovereignty, State Department spokesman P.J. Crowley told reporters at his daily briefing.

But ... we respect that these are judgments for (the) Lebanese government to make, he added.

Sunni Arab countries are concerned about Shi'ite Iran's rising influence in the region, through its proxies of Hezbollah in Lebanon and Sunni Islamist Hamas in the Gaza Strip.

Lebanese political sources have said they expect Ahmadinejad to meet Hezbollah politicians and visit Bint Jbeil, a bastion of Hezbollah and a border village that was heavily bombed during the Israeli-Hezbollah war in 2006.

Iran is embroiled in a long-running dispute with the West over its controversial nuclear program, that has sparked rumors of planned Israeli or U.S. military strikes to deter it from acquiring nuclear weapons.

Iran says its nuclear program is for peaceful purposes.

US commanders have warned that military strikes against Iran could spark retaliatory action by Tehran and its allies like Hezbollah and Hamas that could destabilize the region.

(Editing by Cynthia Osterman)