MOSCOW, June 9 (RIA Novosti) - Iranian President Mahmoud Ahmadinejad is likely to win Friday's presidential election, although he may face a runoff against his main challenger to clinch the presidency, polls and Western analysts said.

Ahmadinejad's only serious opponent in the presidential elections is former prime minister Mir-Hossein Mousavi, the 67-year-old president of the Iranian Academy of Arts. Two other candidates, Mehdi Karroubi and Mohsen Rezaei, are also on Friday's ballot.

Ariel Cohen, a senior research fellow for Washington-based Heritage Foundation, told RIA Novosti that if Mousavi wins, his government would be "more pragmatic," adding that according to his sources "Ahmadinejad not only may win, but there may be serious tampering and fraud to ensure his victory."

"The more moderate regime [of Mousavi] may be a much better partner for the United States for the dialogue that Washington is offering to Iran," Cohen said. He pointed out that Mousavi's supporters are younger, more urban and better educated, and use the Internet, including social networking sites such as Twitter and Facebook.

"We also recognize that there are millions and millions of people in Iran that are not part of the 21st-century information revolution and these people also vote," Cohen said.

According to a recent poll of approximately 1,000 Iranians by Washington-based public policy institutes Terror Free Tomorrow and the New American Foundation, some 34% support Ahmadinejad, 14% support Mousavi, and trailing by a large margin are Karroubi with 2% and Rezaei with 1%. The pollsters noted that 27% were undecided.

Hundreds of thousands of supporters of both main presidential candidates rallied in Iran's capital on Monday, exchanging accusations when they met in the center.

Ahmadinejad supporters called his opponent a "liar" and criticized Akbar Hashemi Rafsanjani, a former reformist president who is supporting Mousavi.

In turn, Mousavi supporters chanted "Ahmadinejad bye-bye" and "If they don't cheat, Mousavi will win," Al Jazeera reported.

Ahmadinejad, 52, took office in August 2005.

It is expected that some 90% of Iranians will vote, many after attending Friday prayers and Cohen raised concerns that they would get "recommendations and instructions from the imams on how to vote," which he said could favor Ahmadinejad.

If no candidate receives over 50% of the vote, a runoff election will be scheduled.