The United States has limited diplomatic ties with Syria because of its support for Hezbollah and Hamas, which the U.S. deems terrorist organizations. President Bush has expressed reluctance to seek help from Damascus on Iraq until the Syrians curb that support and reduce their influence in Lebanon.
The White House has sharply criticized Florida Senator Bill Nelson for his recent visit to Syria, espite Nelson's assertion that the meeting was helpful.
Nelson says Syrian President Bashar Assad is willing to help control the Iraq-Syrian border, where foreign fighters cross into Iraq.
Other senators expected to travel to Syria include Republican Arlen Spector of Pennsylvania and Massachusetts' Democrat John Kerry.