BY MOST accounts Syrian President Bashar Assad is a political naif who has repeatedly misread the cues of a changing Middle East and disastrously miscalculated Syria's responses. That's why it's helpful that the message the U.N. Security Council sent to Damascus yesterday was forceful and unambiguous, backed by all 15 of the council's members in a session attended by a dozen foreign ministers. The council's resolution requires Syria to detain and provide for questioning anyone deemed by U.N. investigators to be a suspect in the assassination of former Lebanese prime minister Rafiq Hariri -- a crime that has been compellingly linked to Mr. Assad's regime. Surely even this dim dictator must now understand that his choices are to dramatically break with his past or risk isolation and sanctions he could not easily survive.

Compliance won't be easy for Mr. Assad, even if he chooses to cooperate. Among the prime suspects in the killing of Mr. Hariri, who was resisting a crude effort by Mr. Assad to reinforce Syria's domination of Lebanon, are the president's brother and brother-in-law. Brother Maher Assad commands the elite Republican Guard forces that are Mr. Assad's last line of defense against a domestic rebellion; brother-in-law Asef Shawkat is the chief of military intelligence. The resolution gives U.N. investigator Detlev Mehlis the prerogative of determining where and under what conditions suspects will be questioned, and Mr. Mehlis may want to transport Mr. Assad's relatives or other suspects out of Syria. He should also interview Mr. Assad himself, since, according to the preliminary report, Mr. Assad directly threatened Mr. Hariri at a meeting several months before his death.

If Mr. Assad ordered the killing of Mr. Hariri, cooperation might only ensure his own trial before an international tribunal. If he did not, he will have to turn on those who did conspire, even if that means breaking with family members and close collaborators. Either way, his best hope of redemption with the outside world may lie in rapidly liberalizing his authoritarian government and reversing his foreign policies, which include backing Iraqi insurgents and Islamic terrorists, supporting extremist Palestinian groups, and using murder and intimidation to destabilize Lebanon.

More likely Mr. Assad will choose, like Saddam Hussein before him, to stall and prevaricate in the hope that the Security Council will shrink from taking action against him. The Bush administration was obliged to drop mention of sanctions from yesterday's resolution in order to win the votes of several governments, including Russia and China. And there is no shortage of Western apologists for Mr. Assad, who claim that he is a victim of hard-liners around him, or that the United States and Europe would be better off striking a deal with him than supporting action that might "destabilize" his country. The regime they would accommodate murdered the prime minister of a neighboring state and has done its best to sow chaos and kill Americans in Iraq. There are better ways to handle it than backroom bargaining: As a start, the United States and its allies should continue to insist that the murderers of Mr. Hariri be brought to justice.