The White House said Thursday that Democratic Sen. Bill Nelson's trip to Syria was not only inappropriate, but that it gave undue legitimacy to a government that is thwarting democratic reform in the Middle East.

Nelson emerged from a meeting with Syrian President Bashar Assad in Damascus on Wednesday, saying Assad was willing to help control the Iraq-Syrian border. The Florida Democrat said he viewed Assad's remarks as "a crack in the door for discussions to continue. I approach this with realism, not optimism."

But White House press secretary Tony Snow said the trip by Nelson, a member of the Armed Services and Foreign Relations committees, and future visits to Syria expected by Sens. John Kerry, D-Mass., Christopher Dodd, D-Conn., and Arlen Specter, R-Pa., send an unhelpful, mixed message to the Syrians.

"We want to make sure that they understand that just because they have visitors does not mean that the position of the United States government has changed," Snow said.

And he warned that the lawmakers could become ensnared in efforts by Damascus to burnish its image.

"It may cost some people their credibility," Snow said. "Sen. Nelson went and thought that he gotten concessions out of Bashar Assad two years ago, and he came back empty-handed."

The bipartisan Iraq Study Group recommended that the administration engage in direct talks with Syria, but President Bush has reacted coolly to that suggestion.

"The point is that even lending a further specter of legitimacy to that government undermines the cause of democracy in the region," Snow said about Nelson's trip.

The United States has limited diplomatic ties with Syria because of its support of Hezbollah and Hamas, which the United States considers terrorist organizations. President Bush has expressed reluctance to seek help from Damascus on Iraq until the Syrian government curbs that support and reduces its influence in Lebanon.

"The Syrians should have absolutely no doubt that the position of the United States government is the same as it has been," Snow said.