WASHINGTON — Over 60 dramatic hours ending yesterday, events in the Middle East highlighted the hopes and risks of change in the region as the Bush administration pursues its agenda of reform.

In Lebanon, an unpopular, Syrian-backed government was brought down by pressure from the streets. In Egypt, the head of a one-party state loosened his decades-old grip on power by announcing plans for multiparty elections. In Syria, an authoritarian regime handed over Saddam Hussein's half brother to Iraqi authorities.

Within the administration, the developments were quietly hailed as signals that the president's vision to spread democracy in the Middle East was not naive and misguided, as critics claim, but an idea Arabs want to embrace.

Despite this windfall, however, Middle East specialists inside and outside the administration remained cautious.

"I've been working on the Middle East too long to be crowing from the rooftops that we've won," a senior State Department official said.

If any proof for that prudence were needed, it came early yesterday in Iraq, when a suicide car bombing south of Baghdad left at least 115 people dead and at least that many wounded in one of the deadliest attacks since the U.S.-led invasion in March 2003.

William Quandt, a White House adviser in the Carter administration during the late 1970s — also a time of hope in the region — said he was heartened by the sight of thousands of Lebanese taking to the streets of Beirut demanding free elections and the withdrawal of Syrian forces from their soil. But he added: "It's unsure where this will lead."

The largest, best-organized opposition group in the country, he said, was the Shiite Muslim fundamentalist group Hezbollah. The organization, backed by Syria and labeled terrorist by the State Department, is strenuously anti-American, yet an important player in Lebanese politics. As a major supplier of social services to the country's large Shiite population, Hezbollah likely would poll well in any free elections.

In Egypt, President Hosni Mubarak's decision to allow his country's first direct, multiparty presidential election later this year also could complicate the U.S. agenda in the region, even though a senior administration official yesterday called it a "positive and welcome step."

A truly democratic election in Egypt could result in major gains for fundamentalist groups, including the banned Muslim Brotherhood, also strongly anti-American, some specialists said. Backers of Bush's efforts to spread democracy in the region counter that strengthening fundamentalist groups is a risk the United States must be willing to take.

Support for stable, authoritarian regimes in the region — the hallmark of U.S. policy for much of the past generation — has produced a contempt for the United States that today drives Islamic terrorist groups, these sources said.

Although Mubarak has frustrated U.S. policy-makers by opposing political reform in Egypt, he is widely believed to have been largely supportive of U.S. policy in the region, especially in the search for a settlement of the Israeli-Palestinian conflict.

Quandt recalled how, during his tenure at the White House, President Carter had nudged the shah of Iran to loosen his hold over the country's political system and how, after the shah's fall, some of the administration's most respected experts on Iran predicted the Ayatollah Ruhollah Khomeini would be a Gandhilike spiritual adviser to a moderate new Iranian government.

"You get something that looks pretty good at the time, but then it eventually turns out very differently," he said.

U.S. policy-makers have had a hint of what free elections can produce in a region where the nation's image is poor and its agenda often viewed as a Zionist-led conspiracy to subjugate Muslim people. January's election in Iraq produced an Islamic scholar with past ties to Iran — Ibrahim al-Jaafari — as the front-runner to lead a transitional government in Baghdad.

Despite these concerns, U.S. officials were moving quickly yesterday to keep up the momentum toward political reform. "The resignation of the [Omar] Karami government represents an opportunity for the Lebanese people to have a new government that is truly representative of their country's diversity," White House spokesman Scott McClellan said. "We will do everything we can to support the Lebanese people."

State Department officials, who declined to be identified by name, said the street protests in Beirut provided the administration with important new leverage to force the withdrawal of 15,000 Syrian forces that entered Lebanon in spring 1976.

Syria has resisted such a pullout on the grounds that its forces were required to maintain stability in a country torn by civil war.

"Today's events prove that the status quo is untenable and that the way forward is to implement the Security Council resolution," a senior U.S. official said. A U.N. Security Council resolution calling for the withdrawal of foreign forces from Lebanon and for free and fair elections was passed in December 2004 under the co-sponsorship of the United States and France.

The protests that led to the Karami government's resignation stemmed from anger that erupted late last month after the assassination of Lebanon's popular former prime minister, Rafik Hariri. While it remains unclear who carried out the killing, Syria's involvement is widely suspected.

After the developments in Lebanon and Egypt, administration officials also are taking a more intensive look at initiatives designed for the region that focus on broadening participation in the political process. "It makes the message [of democratic reform] sound far less Western in its orientation," a senior administration official said. "It shows there are voices in the region, that there is a popular will for change."

Said a second senior U.S. official: "The theory [behind Bush's democratization policy] has always been that if this were to work, it wouldn't be exclusively because we were standing at the top ... hectoring people, but because there would be pressure from within and pressure from below in these societies."

Times staff writers Edwin Chen and Sonni Efron in Washington contributed to this report.