Successful elections in Iraq and the Palestinian territories in January have been followed by tentative changes in Egypt, Qatar and Saudi Arabia and a popular street uprising in Lebanon that toppled an unpopular government. With the encouragement of the American president, reformers across the region are applying escalating pressure on regimes to loosen their grip over autocratic societies.

The rapid pace of developments has surprised even Bush advisers and silenced or even converted some skeptics in Washington less than two months after the president opened his second term with an inaugural address setting the goal of "ending tyranny in our world." As he prepares to give another major speech today to mark the progress, Bush has been in a buoyant mood, aides said, seeing the recent moves as vindicating his expansive vision. "He feels validation," said one aide.

How much the president influenced events driven by indigenous forces on the ground remains a point of debate here and in the region. Some diplomats, analysts and intelligence officers with long experience in the region worry that the Bush team is celebrating too soon and overestimating its ability to steer the change it is helping to set loose. Reforms have been announced in the Middle East in the past only to prove hollow in reality. And the U.S. government has rarely built the sort of sustained effort that many believe will be required to ensure that genuine change takes root.

"What's happening in the Middle East is both hopeful and precarious," said Samuel R. "Sandy" Berger, who was national security adviser to President Bill Clinton. Homegrown pressure for change combined with the purple-fingered success of the Iraqi elections "have raised the heartbeat of reform in the region. It's still a very tenuous situation. There's obviously both hope and danger."

But the White House sees a chance to seize a rare opportunity, and aides said Bush plans to use today's address at the National Defense University to highlight the progress, offer praise for the steps taken so far, and gently prod Cairo and Riyadh in particular to move further to liberalize their countries.

"There is an element of snowball effect here," said a senior administration official, who spoke on the condition of anonymity. "There's now some momentum, and I think we . . . and democracies all around the world are now pushing this a little bit harder. There's a kind of virtuous cycle here, because with each success more and more people want to join, and secondly more people in the democratic world want to join the project."

The cascading images of democracy in the region have made these particularly heady days for Bush, who began talking about Middle East democracy in his first term with little evident success. Aides were thrilled with a Newsweek cover story on Lebanon's so-called Cedar Revolution headlined "People Power," followed by a secondary headline that said "Where Bush Was Right."

The debate in Washington has shifted as well. Jon Stewart, a liberal talk show host on Comedy Central, raised the idea last week that maybe Bush was right. "This is the most difficult thing for me, because I don't care for the tactics," he said, "but I've got to say I've never seen results like this ever in that region."

His guest, former Clinton national security aide Nancy Soderberg, author of a new book critical of Bush policy, generally agreed: "There is a wave of change going on, and if we can help ride it in the second term of the Bush administration, more power to them."

Still, the changes of the past few weeks will be meaningful only if they lead to more, analysts said. Saudi Arabia permitted voting by men for some seats on municipal councils, but women were barred from casting ballots and real power remains in the hands of the royal family. Egyptian President Hosni Mubarak announced that he would open up his reelection this year to candidates of other parties, but his government controls which parties are allowed to participate.

"We're getting ahead of ourselves," said Mara Rudman, senior vice president for strategic planning at the Center for American Progress. And the more Bush takes credit, she added, the more counterproductive it will be to genuine popular movements that do not want to be associated with Americans. "Frankly, if we really care about helping the forces of reform in the region, the best way to do it is without our fingerprints."

Lebanon remains a potent study in the complexity of the situation. Last week's popular uprising stemmed from the assassination of former prime minister Rafiq Hariri, widely blamed on Syria, which occupies Lebanon. While Lebanese protesters succeeded in toppling the country's pro-Syrian government, Bush remained unsatisfied with Syrian President Bashar Assad's subsequent announcement of a gradual pullback of 15,000 troops. Aides said Bush will use today's speech to renew his demand for an immediate withdrawal of all Syrian forces and intelligence units from Lebanon.

Even if Assad were to comply, many diplomats and intelligence officers worry about what would come next. Lebanon is a complex society of multiple sects with a shaky order that could unravel in the vacuum left by a Syrian withdrawal. Various players pursue conflicting goals.

"If Bush fails to comprehend those subtle nuances, and makes the fatal mistake of arrogantly portraying a Syrian withdrawal in Lebanon as a personal triumph for himself in his 'War on Terror' and his 'Spreading Democracy' campaign -- the fruits may turn out to be very bitter indeed," Ray Close, a former CIA officer who served in Lebanon and elsewhere in the Middle East, wrote in an analysis sent to colleagues. "We are again tampering here with a very fragile structure."

Similarly, many current and former U.S. policymakers remain wary of what would eventually replace Mubarak or the Saud family, who have been close U.S. allies over the years. Genuine democratic governments might be dominated by anti-American extremists.

"This is going to take a great deal of intelligent handling," said Edward Djerejian, a former ambassador to Syria and assistant secretary of state for the Near East. "We want the march to freedom to happen in the Middle East but we don't want unintended consequences where in these changes the wrong people come to power. . . . That is not a formula for stasis. On the contrary, we should continue to encourage vigorously political and economic change."