By ALI AKBAR DAREINI

Associated Press Writer

TEHRAN, Iran (AP) - The contrasts were vivid: Pro-government supporters chanted ``Death to America'' and stomped on U.S. flags Wednesday while not far away, hundreds of opposition protesters denounced Iran's leaders and appealed to America's president to choose sides.

``Obama, Obama, you are either with them, or with us,'' the anti-government protesters chanted in Farsi, in an amateur video clip widely circulated on the Internet.

The new and startling appeal to President Barack Obama came as Iran's opposition protesters returned to the streets in large numbers for the first time in nearly two months. Authorities were ready with the same sweeping measures they used to quell fierce election-fraud protests this summer and early fall: Sending paramilitary units to key locations to fire tear gas and beat people with batons.

Witnesses said they heard a man, apparently working for a paramilitary group, shout ``Beat him up, beat him up,'' as he chased a protester in the crowd. ``How is it possible to see such cruelty,'' another protester cried as he stood on the street, according to the same witnesses, who spoke on condition of anonymity because of fear of reprisals.

The protests showed the determination of Iran's opposition to reassert its voice. But the latest marches drew far fewer demonstrators than in the summer or even in September, suggesting the relentless pressure by authorities could be taking a toll.

In Washington, the White House called for an end to the violence against anti-government protesters. White House press secretary Robert Gibbs said Obama administration leaders ``hope greatly that violence will not spread.''

The administration has pursued talks with Iran's government even as it has pushed for more concessions on Iran's controversial nuclear program. Obama said in a statement Tuesday that he wanted the U.S. and Iran to move beyond ``suspicion, mistrust and confrontation.''

The day - marking the 30th anniversary of the U.S. Embassy takeover - has major symbolic importance for Iran's leaders.

Thousands of people attended a pro-government rally called to mark the anniversary, chanting ``Death to America'' and walking over and stomping on U.S. flags outside Washington's former embassy.

Just blocks away, hundreds of opposition marchers in Haft-e-Tir Square denounced President Mahmoud Ahmadinejad with cries of ``Death to the Dictator'' and trampled a poster of Supreme Leader Ayatollah Ali Khamenei, witnesses said.

In all, several thousand protesters joined the marches in various spots across the city. But those numbers were far smaller than at the height of the outrage after claims that Ahmadinejad stole the election by fraud this summer.

The main marches were quickly dispersed by security forces - including paramilitary forces and militiamen linked to the powerful Revolutionary Guard - who used clubs and tear gas, said other witnesses, who spoke on condition of anonymity because of fear of reprisals from authorities.

Mobile phones were disrupted as was Internet access and text messaging, in another echo of the summer. Yet amateur video like the one appealing to Obama still was posted on Web sites, showing protesters in fall clothes and coats in Tehran's streets.

Media restrictions now limit journalists to covering state media and government-approved events, such as the rally outside the former embassy.

Pro-reform Web sites said police fired into the air to try to clear Haft-e-Tir square - about half a mile from the former U.S. Embassy. The report could not immediately be independently verified.

Some demonstrators were injured and arrested, witnesses said, but a clear number could not be independently obtained. There were no reports of serious injuries.

In many ways, it was a replay of the last time opposition groups took to the streets in mid-September to coincide with another state-sponsored rally - that one to denounce Israel. But those marches brought tens of thousands of protesters and a more militant response - with protesters throwing stones and setting fires ablaze.

The smaller turnout raised questions about the long-term stamina of the opposition after facing months of arrests.

``I don't think the opposition is as able to get as many people in the streets as they were after the election,'' said Alireza Nader, an Iran affairs analyst for RAND Corp. in Washington. ``But today's events show there is still opposition that is willing to come out.''

The opposition movement has also evolved since the election fallout touched off Iran's worst internal unrest since the 1979 Islamic Revolution.

Protests still wear the green colors that symbolized the campaign of Mir Hossein Mousavi, who claims Ahmadinejad stole the election from him through rigged ballots.

But it has now expanded into a catchall movement for complaints that include the unlimited powers of the ruling clerics, Iran's sinking economy and its international isolation. Its wider reach has managed to draw in other political leaders and clerics who have challenged Ahmadinejad and his allies.

``I think the long-term crisis for the government isn't over,'' said Nader. ``There is still a strong sense that the Ahmadinejad government is not legitimate.''

A pro-reform Web site said militiamen on motorcycles prevented Mousavi from leaving his office to attend the marches. Another leading opposition figure, Mahdi Karroubi, fell to the ground after being overcome by tear gas, according to a posting by his son Hossein on Karroubi's Web site. Karroubi did not need medical attention, his son said.

The full scope of Wednesday's protests was difficult to determine. Some opposition groups also reported demonstrations in other cities such as Shiraz and Isfahan.

Authorities had warned protesters days in advance against attempts to disrupt or overshadow the annual gathering outside the former embassy, which was stormed by Iranians in 1979 in the turbulent months after the Islamic Revolution.

Fifty-two Americans were held hostage for 444 days, and the two nations have never resumed diplomatic ties.

Outside the former U.S. Embassy, thousands of people waved anti-American banners and signs praising the Islamic Revolution. As in past years, many were students bused in from outside Tehran.

The main speaker, hard-line lawmaker Gholam Ali Haddad Adel, denounced the United States as the main enemy of Iran. He called opposition leaders dangerous to the country.

Associated Press writers Brian Murphy in Dubai, United Arab Emirates, and Lee Keith in Cairo contributed to this report.

11/04/09 19:04 © Copyright The Associated Press. All rights reserved. The information contained In this news report may not be published, broadcast or otherwise distributed without the prior written authority of The Associated Press.