WASHINGTON In 1984, when President Ronald Reagan withdrew U.S. forces from Beirut after a suicide attack killed 244 marines, the conservative Republican and sometime presidential candidate Pat Buchanan said, "It is dangerous to be America's enemy, but fatal to be America's friend."

Since then, the people of Lebanon have had good reason to recall those words. In 1990, President George H.W. Bush traded Lebanese sovereignty for President Hafez Assad's support in the first Gulf War. Kuwait was freed, Lebanon was ceded to Syria.

Today, various regional media outlets report that the sons, George W. and Bashar, may be working on another Faustian deal, an arrangement driven by realpolitik considerations, not ideological convictions.

Bashar Assad, taking a page out of Muammar el-Qaddafi's playbook, is alleged to be negotiating with the Bush administration to protect his regime from the findings of a UN investigation into the assassination of former Lebanese prime minister Rafik Hariri. The car bombing that killed Hariri precipitated protests in Lebanon and around the world that forced an end to Syria's 15-year occupation.

The Beirut spring was a rare and unequivocal success for the Bush administration as it struggled but failed to stem the political chaos and escalating violence next door in Iraq. Bush took a principled stand in a truly multilateral framework. Courageous Lebanese, coupled with support from international community, won Lebanon's independence.

As the last Syrian soldiers crossed the border, however, an insidious campaign began to destabilize Lebanon. Interior Minister Hassan Sabaa has admitted that "a somewhat professional terrorist phantom" is at work. Scores of bombs targeting Christian areas have given rise to vigilante groups and heightened sectarian tensions. In short, the security situation in Lebanon has deteriorated so dramatically that many are taking extraordinary precautions to protect themselves and their families.

Contrast this state of fear with people's fearlessness on March 14, when a million rallied to demand and end to Syria's suffocating presence.

Now, those Lebanese who counted on Bush's support in the spring are increasingly concerned that he has agreed to cut a deal with Assad that would short-circuit the report of the UN investigator, Detlev Mehlis, by granting top officials in Syria immunity in exchange for significant support with Iraq, Lebanon, the Israeli-Palestinian peace process and elsewhere.

This is not just a critical juncture for Lebanon, but for Syria and the United States as well.

To curtail or soften the Mehlis report, particularly if Mehlis's mandate is extended at the end of October, would rob Assad of the opportunity to clear himself. Assad has repeatedly asserted his innocence. If overzealous subordinates are implicated, and the trail stops there, he could rally public support for an overhaul of his own regime. If such a move were accompanied by greater civil liberties and fewer secret police, Syrians would probably back his presidency as he struggled to root out those loyal to Hariri's assassins.

Bush should demand nothing less. If Bashar does not have the power to bring the guilty to justice, the regime in Syria should suffer international isolation and stringent sanctions.

For Bush, the choice is between further eroding American credibility by cutting a deal or even appearing to do so, or reinforcing universal values that remain a beacon to the world's oppressed and powerless. This should be a foreign policy red line: Washington cannot advocate for the rule of law if foreign policy considerations can exempt murderers from prosecution.

Mehlis should be allowed to continue his investigation for as long as he deems it necessary, and without interference or obstruction from either Washington or Damascus. This is not only in Lebanon's interest, but in the interests of Syria and the United States as well. Otherwise, those forces at work destabilizing Lebanon would be emboldened to continue working their way down what Western diplomats allege to be a hit list of Lebanese officials, intellectuals and journalists.

The global campaign of Europe and the United States to end tyranny and instill democracy will be dealt a serious blow if Beirut's spring is as short-lived as Czechoslovakia's was in 1968.

(Edward S. Walker, president and chief executive of the Middle East Institute in Washington, is a former U.S. assistant secretary of state for near eastern affairs.)