IN THE PAST month, heat from the outside world has been slowly rising on the world's remaining Arab Baathist dictatorship -- Syria -- and the result has been a noticeable if somewhat inconclusive bubbling of developments in normally somnolent Damascus. Syria's government has been a longtime sponsor of terrorism, a stockpiler of missiles and chemical weapons, and an unapologetic ally of Islamic extremists; it has allowed hundreds, if not thousands, of insurgents to stream across its borders to fight U.S. forces in Iraq. Until recently it had suffered few consequences, other than economic sanctions that were mandated by Congress. That has begun to change.

In August, Syria's callow and ineffectual president, Bashar Assad, managed to provoke not just the United States but France by forcing neighboring Lebanon to extend the term of its pro-Syrian president. The result was a U.N. Security Council resolution calling for the withdrawal of Syrian troops from Lebanon. Nine days later, a U.S. delegation arrived in Damascus to insist that Syria cooperate with U.S. and Iraqi efforts to control movement across its border. Two weeks later a car bomb, almost certainly planted by Israel, exploded in Damascus and killed one of the Hamas leaders who had been given harbor there. Though it is rare for Israel to carry out such an audacious operation in the Syrian capital, Mr. Assad won scant international sympathy. Instead, U.N. Secretary General Kofi Annan reported to the Security Council that Syria had not met the terms of Resolution 1559, despite its claims to have redeployed 3,000 of its 20,000 troops in Lebanon.

Mr. Assad seems to be getting nervous. Last week he reorganized his government, installing the former top Syrian intelligence general in Lebanon as interior minister. Then he delivered a whining speech warning that chaos would overtake Lebanon if Syrian troops withdrew. Behind the rhetoric, Syrian security forces are trying to appease Washington, promising better controls on the border and acting against some of the organizers of Iraqi resistance operating in Lebanon.

This, of course, is not enough: It merely demonstrates that concerted outside pressure can bring about changes in Syrian behavior. That pressure should be stepped up. The Security Council should renew its demand that Syria withdraw from Lebanon, and accompany it with the threat of sanctions. Arab states, which for decades have insisted on the sanctity of U.N. resolutions about Israel, should be pressed to take a public position on this one. The Bush administration and Iraqi leaders should make it clear that continued infiltration of insurgents and terrorists into Iraq will be considered a hostile act by Syria and subject to the responses usually given an enemy, from the breaking off of relations to -- in the last resort -- military retaliation. There are no reasons for continued toleration of Syria's rogue behavior; instead, there is an opportunity for insisting on change in the Arab state where it is most needed.