EVERYWHERE I traveled throughout the Middle East this winter, the feeling was inescapable that the region could explode at any time. The threat of three simultaneous civil wars that King Abdullah of Jordan spoke of is real, and perhaps the most imminent danger -- in Lebanon -- is the least understood. Lost in the shadows of Iraq, the struggle to save the fragile democracy born of the Cedar Revolution has reached a moment of truth. If America does not act now, this key front in the broader struggle between moderates and extremists for the future of the Arab world will be lost -- and the consequences will long be felt throughout the region. The radicals' ambitions for overthrow move from Prime Minister Fouad Siniora in Lebanon to President Mahmound Abbas in Ramallah to Prime Minister Nouri al- Maliki in Iraq. They are determined to achieve a clean sweep. Anyone who has longed for a George Washington or Thomas Jefferson to emerge and lead the fight for democracy in the Middle East should come to Beirut and meet the patriots who have made incredible sacrifices for a free and independent Lebanon. There is the son of slain former prime minister Rafik Hariri. There is the Cabinet minister whose husband was assassinated soon after becoming president, and the minister of defense, who after 12 surgeries still bears the scars of an assassination attempt. There is the mother of recently slain 34-year-old Lebanese parliamentarian Pierre Gemayel, who said to me simply: "We pay a high price for sharing what you believe in," and ask yourself whether we are paying her the debt owed for our shared beliefs. At the forefront of this struggle is Siniora, the prime minister of Lebanon, who has stood up to a challenge that many extremists thought would bring down his government. Weakened by this summer's war, Siniora is effectively under siege by Hezbollah, which has brought hundreds of thousands of demonstrators to the streets of Bierut and shut down the government with the mass resignation of its ministers. To provide the support he needs, we must recognize and adapt to the new realities on the ground. We've lost 3,000 American lives and invested more than $300 billion in hopes of forcibly birthing democracy in Iraq -- while largely ignoring Lebanon, where democratic institutions already have a foothold. Success there -- and across the Middle East -- ultimately depends more on winning over civilian populations with basic goods and services than defeating armies with sophisticated weapons and technology. New York's street-wise mayor Fiorello LaGuardia proclaimed, "There is no Republican way to clean a street." This is Politics 101: If you don't deliver services, you don't get the support of the people. Yet today, the forces of radicalism are doing a far better job than the moderates in making the most basic connections with restive populations. In Lebanon, Iran has seized the opportunity to win over the population by channeling some $500 million in reconstruction funds through Hezbollah -- over twice as much as we have. In fact, Iran is doing more in rebuilding Lebanon than Washington is doing in rebuilding New Orleans. We must change this dynamic by dramatically increasing economic assistance -- and pressing others in the international community to do the same -- and ensuring that Lebanese see that they can count on their elected leaders. And we must redouble our efforts to strengthen the Lebanese military, which has earned the trust of the people but lacks the strength to confront Hezbollah. The key to Lebanon's future lies in getting Syria to truly respect Lebanese sovereignty. The money and weapons that empower Hezbollah come primarily through Syria, which uses proxies like Hezbollah to advance its hegemonic designs. They must be convinced to change course, including by ensuring that UN Resolution 1701 -- which again calls for the disarmament of Hezbollah -- is fully implemented. To test the Syrians directly, as the Baker-Hamilton Commission suggested, Senator Christopher Dodd of Connecticut and I met with President Bashar al- Assad for more than two hours. The conversation confirmed my belief that engagement with Syria could be useful in advancing our objectives across the region. The Syrian leadership will act according to its own self-interest. The challenge is to get Syria's leaders to make a strategic decision to change direction, and shift their allegiance away from Iran. This requires a package of incentives that will provide real benefits for playing a more constructive role and disincentives that will undermine their interests -- if not endanger their survival -- if they do not. These would be implemented incrementally, based on verified facts on the ground. This comprehensive approach, similar to the one used with North Korea and Iran, must include the full participation of moderate Arab countries like Egypt, Jordan, and Saudi Arabia -- which, like Syria, have largely Sunni populations -- as well as Turkey. There is no guarantee that this approach will save Lebanon and turn Syria into a positive force in the region -- but the current policy only guarantees more of the same. Lebanon teeters on the brink of disaster -- but its leaders refuse to surrender. As Amine Gemayel, the former president of Lebanon, said in explaining why he is running to replace his son in Parliament, "We keep going. We keep fighting. We keep struggling." The question is whether we will be a real partner in this struggle. John F. Kerry is a US senator from Massachusetts.