Hundreds of anti-government rebels in Jeeps and all-terrain vehicles plan to take a protest ride Saturday up an off-limits riverbed in Grand Staircase-Escalante National Monument.

The southern Utah rally offers more evidence that the Bureau of Land Management's leniency against illegal off-road recreationists on the monument may be blowing up in federal faces.

For years, off-roaders have been driving up the Paria River. Now they're angry because of reports that the BLM plans to enforce a ban on off-highway vehicles in the canyon.

The route, which winds through the Paria-Hackberry wilderness study area and a river the BLM says boasts wild and scenic qualities, never has been open to riders. Rather, the agency for nine years has turned a blind eye to illegal motorized use, and even tacitly green-lighted it in a document published two years ago.

This week, bloggers are burning up the Web with anti-environmentalist rhetoric, vowing to show the BLM that the off-road community can be just as aggressive as conservation organizations about their rights to public land.

"This is a stand," Kanab resident and protest organizer Shawna Cox said Wednesday. She expects 500 to 1,000 riders to show up for Saturday's demonstration.

Corey Shuman, who runs Gold Rush Expeditions out of Draper, said in a blog posting that Kane County Commissioner Mark Habbeshaw "will be out Saturday to ride the road, shoulder to shoulder, with his constituents." A Salt Lake Tribune call to Habbeshaw was not returned.

Monument manager Rene Berkhoudt refused to comment on the event. However, his spokesman, Larry Crutchfield, said in an e-mail Wednesday evening that an April 13 ruling from the 10th U.S. Circuit Court of Appeals against Kane and Garfield counties' attempts to ratify their ownership claims to roads that cross federal lands "provides important clarification to this long-standing problem."

The BLM is developing a plan, Crutchfield said, on "how best to implement the travel prescriptions outlined in the monument management plan."

The agency already has acknowledged Jeeps and ATVs don't belong in the area. In 2007, it issued a report for managing the Paria River and Sheep Creek -- along with their side canyons -- that said the 2000 monument plan prohibited motorized access in the corridors.

But because the counties had sued over access, the BLM said, monument managers would seek "voluntary" compliance. "Visitors choosing not to participate in the voluntary closure should follow 'Leave-No-Trace' and 'Tread Lightly' practices to minimize potential negative impacts to resources," the 2007 publication says.

The BLM's lawsuit explanation was a dodge, conservationists argue, because the federal courts never told agency officials to avoid enforcement. "They took it upon themselves," said Phil Hanceford, a legal analyst for The Wilderness Society, "to abstain from following the management plan."

Cox said BLM officials won't stop Saturday's protest ride. "They want us to be cautious and make sure we follow the rules, and we are," she said. "When the BLM works with us, it works. My heartburn is people in the environmentalist community ... when 90 percent of their membership is from China."

Liz Thomas, a Moab-based attorney with the Southern Utah Wilderness Alliance, said the ride would be flat out against the law. (And "not one" of SUWA's members, she added, is from China.)

"They're driving illegally in a [wilderness study area]," Thomas said. "This has been a WSA since the original inventory during the late 1970s and early 1980s."

To add protection, she noted, the BLM's monument plan overlaid the WSA with a "primitive zone" designation, which bars motorized and mechanized access.

And it's not a road, Thomas said, it's a river. The riders probably will be in water the whole way, given that it's spring-runoff season.

Several YouTube postings show 4x4 riders crossing the riverbed, shooting huge rooster-tail wakes into the air as they go. A blog site contains photos of a ride through the river in winter, including a shot of a 4x4 stuck in snowy quicksand.

Crutchfield's e-mail said nothing about whether the BLM would be present Saturday to enforce the ban. But it's not as if the agency is never willing to crack down.

Washington County OHV rider Dan M. Jessop was slapped with a $300 fine in 2006 for leading a group of off-roaders through a BLM-closed route in a southern Utah wilderness study area.

More recently, the agency helped investigate a case for the Justice Department against Tim DeChristopher, a University of Utah student who falsely bid at a December oil and gas lease auction to protest federal land-use policies. DeChristopher was arraigned last week on two felony counts.