Increasingly, officials say, Syria is to the Iraq war what Cambodia was in the Vietnam War: a sanctuary for fighters, money and supplies to flow over the border and, ultimately, a place for a shadow struggle.

But other officials, who say they got their information in the field or by talking to Special Operations commanders, say that as American efforts to cut off the flow of fighters have intensified, the operations have spilled over the border - sometimes by accident, sometimes by design.

Some current and former officials add that the United States military is considering plans to conduct special operations inside Syria, using small covert teams for cross-border intelligence gathering.

American officials say Mr. Bush has not yet signed off on a specific strategy and has no current plan to try to oust Mr. Assad, partly for fear of who might take over.