Syria, which withdrew its troops from Lebanon six weeks ago, remains in such tight control of their shared 240-mile border that Iranian arms bound for Hezbollah's militia continue to move freely through Syria into Lebanon, according to senior administration officials and diplomats familiar with the operations.

The ongoing flow of arms would violate U.N. Resolution 1559, which calls for Syria to withdraw all troops and intelligence agents from Lebanon and the disarming of Hezbollah, the last major Lebanese militia. Iran's arming of Hezbollah, including Katushya rockets that have been fired into Israel, began more than two decades ago.

Despite angry Syrian denials, international alarm about Syria's renewed intervention in Lebanon deepened yesterday, with Secretary General Kofi Annan telling United Nations envoys that he had decided to send a verification team back to Lebanon to look for a renewed Syrian presence.

President Bush said he is "disturbed" by reports of Syria's renewed intervention in its small neighbor, especially a reported Syrian "hit list" of at least four prominent Lebanese politicians and the return of Syrian intelligence operatives.

The list included a senior Lebanese political leader who allegedly was to be targeted this month, according to a well-placed source not in the United States who is familiar with the list and requested anonymity because of the sensitive intelligence. The information had generated "enormous concern" in the international community about a new Syrian campaign to destabilize Lebanon, the source said.

Bush said the United States and its allies will investigate, "and we expect the Syrian government to follow up on these troubling reports.

"Our message to Syria, and it's not just the message of the United States -- the United Nations has said the same thing -- is that in order for Lebanon to be free, is for Syria to not only remove her military but to remove intelligence officers, as well," Bush told reporters during an Oval Office meeting with South Korean President Roh Moo Hyun.

Syrian Ambassador Imad Moustapha yesterday denounced the allegation as "inaccurate and unfair. . . . Its credibility is equal to the U.S. claims on Iraqi weapons of mass destruction," he said in an interview. "We would not be so stupid as to send agents to give a pretext to the administration."

Moustapha said the hit-list allegation is part of a broader U.S. attempt to malign Syria. "Every couple days, the administration comes up with a new story about Syria," he added. "It has nothing to do with Syria, but with U.S. policy toward the Mideast. If you remember since the early days of war on Iraq, every three or four days, we had a story about Syria -- like Saddam Hussein and sons were hiding in Syria. We are so tired of these accusations. . . . They want to find a scapegoat for their own failures in Iraq and elsewhere."

Moustapha also said Syria is willing "at the highest level" to engage with the United States, adding that Washington had repeatedly rebuffed Syrian offers to cooperate on Iraq, including information exchanges and border patrols.

The White House welcomed the decision to send the U.N. team. "We want to see them there through the period of the elections and cabinet formation in order to better clarify reports of Syria's continued intelligence presence and to deter any further efforts to derail that democratic process that is underway," White House spokesman Scott McClellan said. Lebanon's four-phase election ends on June 19.

McClellan said the United States had been hearing "for some time about Syrian hit lists, targeting key Lebanese public figures of various political and religious persuasion, for assassination."

U.S. sources also said the return of known Syrian intelligence operatives has been recent.

Annan dispatched U.N. envoy Terje Roed-Larsen for talks this weekend in Syria. Moustapha said the U.N. envoy to Lebanon will meet with Syrian President Bashar Assad tomorrow. In contrast to earlier visits, Roed-Larsen he is scheduled to go only to Syria, not Lebanon or other Arab states.