Syria and Iran know how badly the United States wants their cooperation to stabilize Iraq, and they’re setting a high price.

Part of that price was made brazenly clear in Beirut on Tuesday – where a key anti-Syrian cabinet minister, Pierre Gemayel, was shot dead in broad daylight. The price looks far higher than the United States can or should pay.

Gemayel was killed on the day the U.N. Security Council was set to endorse an international tribunal to investigate a previous assassination – of Lebanon’s former Prime Minister Rafik Hariri in February 2005.

The early phase of a U.N. probe into Hariri’s death implicated top Syrian officials, along with their Lebanese henchmen. The head of the U.N. probe, former Belgian prosecutor Serge Brammertz, will issue another report in December; Syrian officials might one day stand before the tribunal. The implication of his regime in such a murder would threaten the survival of President Bashar al-Assad; the Syrians clearly want to avoid such a trial.

Although Syria denied involvement, yesterday’s killing looks like a warning to Washington and to the pro-Western Lebanese government. Damascus knows the Bush team needs help in its efforts to salvage Iraq. It wants Washington to drop its support for the tribunal in return.

The Syrians have also been sending signals to Beirut that the Americans can’t protect government members, and they’d better resign themselves to Syrian – and Iranian – overlordship. Gemayel is but the latest in a string of prominent anti-Syrian Lebanese killed over the past year.

The plight of Lebanon’s brave government is particularly tragic, even in a gloomy Middle East. This government, led by the courageous Prime Minister Fuad Siniora, is the one democratic success story in the region, a Cedar Revolution born from the upheaval caused by the killing of Hariri. Lebanese and international outrage at his death – which most Lebanese blamed on Syria – led to the expulsion of Syrian troops from Lebanon. Syria was isolated internationally.

But the weakened Syrians soon struck back.

While Lebanese elections returned a pro-Western government, Lebanon’s Shiites cast a sizeable minority of votes for the radical Shiite movement, Hezbollah, an ally of Syria and Iran. Hezbollah leaders received a huge boost after they kidnapped two Israeli soldiers, when Israel’s retaliatory air war failed to defeat their fighters.

The White House missed a chance to strengthen the Siniora government during Israel’s air war. Early on, when Hezbollah was reeling, the Beirut government sought U.S. support for an end to the bombing and an international cash transfusion for rebuilding. Hezbollah had agreed to an unprecedented Lebanese cabinet resolution to disarm and might actually have been pressured to begin. Instead, the White House backed continued Israeli bombing of Lebanon’s roads, bridges and villages, which failed to dislodge Hezbollah and undercut Siniora’s hand.

Meantime, as the prospect nears of an international tribunal, Hezbollah has been trying to bring down the Siniora government in favor of one it could control.

Hezbollah pulled its members and allies out of the cabinet, shrinking the number of ministers to the point at which two more defections would collapse the government. The murder of Gemayel has reduced that margin to one. Every Lebanese cabinet minister must now be wondering if he will survive the week.

The Bush team is in a bind. It needs Syrian and Iranian cooperation but must not abandon the Cedar Revolution. Nor can it abandon the U.N. probe to find the killer of Hariri.

Now that the Security Council has approved the proposal for a tribunal, the Lebanese parliament must vote it up or down. Via phone to Beirut, I asked independent Lebanese parliament deputy Misbah al-Ahdab, a supporter of the Siniora government, what would happen: “We have the majority,” he said. “The tribunal will be endorsed.

“I think the United States should be firm on an international tribunal and firm on not accepting any new government in Lebanon,” he continued. “This is the hijacking of a country.”

Ahdab said there’s nothing wrong in talks between the United States and Syria. But Damascus must know that “Lebanon is not the price paid” for getting Syria into such talks, and that “the tribunal is still on.”

This is the near-impossible balance the Bush team must seek if it is to avoid the Iraqi-ization of Lebanon: talking to Iran and Syria without betraying the Lebanese.

Trudy Rubin is a columnist and editorial board member for The Philadelphia Inquirer.