BEIRUT, Oct 13 (Laila Bassam/Reuters) - Thousands of Lebanese Shiites gave Iran's President Mahmoud Ahmadinejad a tumultuous welcome on Wednesday at the start of a visit which has highlighted Western fears about Tehran's growing influence in Lebanon.

Throwing rice and flowers at the smiling Iranian leader, who waved from the open roof of his car, they lined the main road from Beirut airport to the presidential palace where Ahmadinejad was due to meet Lebanon's President Michel Suleiman.

Iranian flags, banners, balloons and posters of Ahmadinejad were draped along the route -- as well as pictures of Iran's spiritual leader Ayatollah Ali Khamenei and the founder of Iran's Islamic Republic Ayatollah Ruhollah Khomeini.

Ahmadinejad's visit has raised concerns in Washington, which wants to isolate Iran over its nuclear programme and says Iran's support for Hezbollah militants undermines Lebanese sovereignty.

The visit has also alarmed pro-Western politicians in Lebanon's fractious unity government, which includes Hezbollah ministers. The government is already deeply split over an international investigation into the killing of former premier Rafik Hariri which is expected to indict Hezbollah members.

Lebanon's largest parliamentary bloc, led by Hariri's son, has condemned Ahmadinejad for treating their country as an Iranian base on the Mediterranean.

But most Shiites are grateful for Iranian support to Hezbollah, which fought a 34-day war with Israel in 2006, and for the support Tehran has given to reconstruction since then.

He stood by us during Lebanon's troubles, and the 2006 aggression. It's not much to stand here to welcome him -- even if we had to stand for two whole days, 50-year-old Mahmoud Darwish said as he waited with his son to greet Ahmadinejad.

He helped us rebuild Lebanon. If he hadn't, our houses would still be destroyed and we would still be living in tents.


BORDER VISIT

Ahmadinejad, who has called for Israel to be wiped off the map, is expected on Thursday to visit southern Lebanese towns near Israel which were heavily bombed in the 2006 conflict.

Officials close to Hezbollah say they have spent about $1 billion of Iranian money since 2006 on aid and rebuilding. The West accuses Iran of supplying arms to Hezbollah, which says it has an arsenal of more than 30,000 rockets.

Iran has also offered to help Lebanon boost its inadequate electricity network, support water projects, and supply its poorly equipped army after U.S. military aid was held up in August by political objections in Congress.

Ahmadinejad will hold talks with Prime Minister Saad al-Hariri, a Sunni Muslim, and the Shi'ite speaker of parliament Nabih Berri on Wednesday. He will also address a rally in south Beirut at which Hezbollah Hassan Nasrallah is due to speak -- possibly by video link. (Writing by Dominic Evans; Editing by Alistair Lyon and Louise Ireland)