Sunday's unusual action by Congress gave the parents of Schiavo the right to sue in federal court over the withdrawal of life support from their severely brain-damaged daughter - trumping the judgments of Florida courts and the wishes of Schiavo's husband- guardian. Although the move raises a wide range of complex constitutional questions and could ultimately require the Supreme Court's involvement, Schiavo's parents face a daunting array of legal obstacles in persuading federal courts to involve themselves in an area of state authority.

``There are so many substantial hurdles that the case has to get over that it's hard for them not to trip on one,'' said Michael Dorf, a constitutional law professor at Columbia University.

Alan Meisel, who directs the University of Pittsburgh's Center for Bioethics and Health Law, called it ``very, very unlikely'' that Schiavo's parents will prevail.

The difficulty showed itself immediately Monday when attorneys for Schiavo's parents, Bob and Mary Schindler, filed their request for an injunction in U.S. district court. They argued that the federal court should rule that the Florida judge's order to remove Schiavo's feeding tube ``violates and continues to violate'' her constitutional rights of religion and due process. That request is at odds with the law signed early Monday by Bush directing the federal courts to consider the case de novo - without taking into account the state court's findings.

The judge assigned to the case, James D. Whittemore of Tampa, expressed skepticism about the Schindlers' lawsuit. ``I think you'd be hard-pressed to convince me that you have a substantial likelihood'' of success, he said.

Early Tuesday, Whittemore rejected the parents' emergency request under that legislation to have the tube reconnected, saying they had not established that they would probably prevail at a trial on their claim that Schiavo's religious and due process rights have been violated.

Schiavo's parents then appealed to the 11th U.S. Circuit Court of Appeals in Atlanta.

Precedents Have Been Set

The lawyers for the Schindlers need to weave their way around some difficult Supreme Court precedents. The 1990 Cruzan case made clear that a person in a persistent vegetative state had a constitutional right to be removed from a feeding tube. In a 1997 ruling, Chief Justice William Rehnquist affirmed that the Cruzan case assumed that ``the due process clause protects the traditional right to refuse unwanted lifesaving medical treatment.'' And in the 1995 Plaut ruling written by Justice Antonin Scalia, the court struck down an effort by Congress to direct courts to reopen final judicial judgments.

Thus, even if the case goes to the Supreme Court, some of the conservative justices who might have the most sympathy for the Schindlers' claim have in the past sided with the states on similar cases. ``I don't think the chance is much above zero'' that this will change now, said Bruce Fein, a constitutional lawyer and columnist for the Washington Times.

Congress' Authority

Article Three of the Constitution gives Congress the authority to send a case to federal courts particularly if a person's constitutional rights have been violated. However, it is not clear that Congress can dictate guardianship rules to states. ``I don't think any power Congress has under the Commerce clause or other powers gives them the authority to make federal guardianship laws,'' said Mary Cheh, a law professor at George Washington University.

Information from The Associated Press was used in this report.