A federal appeals court has upheld a lower court decision that a large white cross sitting on federal land in the Mojave desert violates the constitutional guarantee of separation of church and state and should be removed.

The American Civil Liberties Union sued the National Park Service in 2001 on behalf of a retired park employee. A federal judge sided with the ACLU and ordered the cross, in the Mojave National Preserve near the California-Nevada border, be taken down.

The Department of Justice appealed the lower court's decision to the U.S. Court of Appeals for the 9th Circuit. Rather than remove the cross, the Park Service threw a large tarp over the structure while the case was in court.

Monday's opinion did not specify whether the cross should be removed immediately or could remain covered if the case is appealed to the Supreme Court.

"The [9th Circuit] said this case is really quite simple. Using a sectarian religious symbol is not permissible on federal land," Peter Eliasberg, managing attorney for the ACLU of Southern California, said. "Sometimes you just have to hit them over the head three, four or five times."

A spokesman for the Justice Department said attorneys are reviewing the ruling to determine whether to appeal.

The Veterans of Foreign Wars erected a cross in 1934 in memory of those who fought and died in World War I. A plaque explaining the cross's purpose was placed at the foot of the structure, but the sign disappeared long ago.

After being nearly destroyed several times, the cross -- originally two pieces of wood nailed together and planted in the desert -- has been changed several times. The latest version is made of two metal pipes welded together and painted white.

Officially designated as a war memorial by Congress, the cross has also been the site of Easter sunrise services over the years. In 1999, the National Park Service denied a request to build a Buddhist religious symbol near the cross.

Eliasberg scoffed at the government's argument that the site is a war memorial. "That doesn't honor Muslim veterans, Jewish veterans, atheist veterans or agnostic veterans," Eliasberg said. "It's a preeminent symbol of a religion. If we want to have a war memorial on federal land, the government certainly knows how to do that without using a divisive sectarian religious symbol."

Rep. Jerry Lewis (R-Calif.) crafted a plan to keep the cross in place by transferring the patch of land where the cross sits to the VFW in exchange for five acres of privately owned land elsewhere in the preserve. The legislation was approved earlier this year, but the transfer has not been completed.

Because the land transfer would put the cross on private, not public, land, the government argued that the issue of separation of church and state is moot, and urged the court not to rule in the case.

But Circuit Court Judge Alex Kozinski, who wrote Monday's opinion, said the transfer could take years to complete and provisions in the legislation could allow the land to be transferred back to the government, putting the cross back on public land.

"This case is not yet moot and may not be for a significant time, as defendants conceded that the land transfer could take as long as two years to complete," Kozinski said in a 14-page opinion.

A spokesman for Lewis said the lawmaker would support an appeal to the Supreme Court, but he hopes the land transfer would make that unnecessary.

The ACLU has also challenged the constitutionality of the land swap.