LOS ANGELES - The Department of Homeland Security is ahead of schedule in building some 700 miles of fencing along the Mexican border, but some environmental groups, elected officials and local Indian tribes say too little attention is being paid to the environmental consequences of the barriers.

In the latest flash point, Homeland Security Department officials took possession of land last week in the Buenos Aires National Wildlife Refuge in southern Arizona by brokering a land swap with another federal agency, the Fish and Wildlife Service.

Opponents say the 12-to-15-foot-tall steel fence and its construction will disrupt the habitat of jaguars, pygmy owls and other sensitive fauna in the wildlife refuge, and encourage illegal immigrants to use more remote, ecologically delicate terrain.

Three times, including twice this year, Homeland Security Secretary Michael Chertoff has exempted fence construction along the border from environmental reviews normally required for such projects, saying the waivers avoid legal delays that threaten speedy completion.

Officials at the Fish and Wildlife Service said they believed Mr. Chertoff could have issued a similar exemption in the Buenos Aires case if they had not negotiated the land swap. The Fish and Wildlife Service’s manager of the refuge had issued a document that declared the fence would have no significant impact on the refuge, but rescinded that declaration several weeks before the land swap was agreed upon.

“This is another example of the federal government riding roughshod over America’s treasured lands and legal process in its rush to complete a highly ineffective and controversial border wall,” said Matt Clark, the Southwest representative for Defenders of Wildlife, an advocacy group.

Federal officials have defended the land swap and the environmental waivers, saying speedy construction of the fence will help lead to control of the border and reduce trash and other environmental damage generated by illegal immigrant traffic.

The land swap at the Buenos Aires refuge involved 5.8 acres along a seven-mile stretch at Sasabe that has been a major illegal crossing point. A spokesman for the Fish and Wildlife Service said the deal was not intended to bypass the decision by the then-refuge manager in October to withdraw his assessment that the fence was compatible.

The manager, Mitch Ellis, did not respond to a telephone message. But in an interview last week with The Arizona Daily Star he objected to the way the fence decision was being carried out.

“Nobody did anything wrong except that we sort of hid the process,” Mr. Ellis told the newspaper, “and I’m not sure why we did it that way.”

Jose Viramontes, a spokesman for the Fish and Wildlife Service, said the swap was the “win-win” solution to overcome potential environmental damage on the land and regulatory difficulties in building on it.

“The fence gets built, the D.H.S. meets its mission, and we acquire valuable land,” Mr. Viramontes said. The land being given to the Fish and Wildlife Service in exchange for the 5.8 acres has not yet been identified.

Mr. Chertoff first used his waiver power, granted to him under the REAL ID Act of 2005, to speed the construction of fencing in 2005 on disputed land in San Diego. The other decisions came in January and in October of this year, both on tracts in Southern Arizona.

Defenders of Wildlife and the Sierra Club are challenging Mr. Chertoff’s waiver power through an amended federal lawsuit arising from his decision in October to overrule environmental review for a stretch of fence on the San Pedro Riparian National Conservation Area in southeastern Arizona. The lawsuit is pending in federal court.

In addition, Representative John D. Dingell, Democrat of Michigan and chairman of the House Energy and Commerce Committee, has asked Mr. Chertoff in a letter for a detailed explanation by Wednesday of why he needed to invoke the waiver for the San Pedro fence.

Mr. Chertoff has said the fencing, in addition to thousands of new Border Patrol agents and presence of thousands of National Guard troops, has resulted in a 22 percent drop in apprehensions of illegal immigrants along the border, though economists and political scientists on the border say several other factors could be contributing to the decline.

A spokeswoman for the Homeland Security Department, Veronica Nur Valdes, said that when the department has waived environmental review it has included some features in the fencing to answer environmental concerns, like including tiny holes to allow lizards and other animals through.

While plans for a “virtual fence,” a test project involving integrated high-tech cameras and sensors, have been delayed for months by technical glitches, physical barriers are going up quickly and are remaking stretches of vast border wilderness.

In the past year, the government has built 270 miles of pedestrian and vehicle fencing, including 76 miles of pedestrian fencing, exceeding a goal of 70 miles, for a total of 106 miles of such barriers along the 2,000-mile Mexican border.

Most of the vehicle barriers do little to stop individuals on foot, but they impede cars and trucks from driving loads of people across.

Next year, the department plans to add 225 miles of pedestrian fence, for a total of 370 by the end of 2008, in addition to several hundred miles of vehicle fencing.

Officials said total fencing would amount to 670 miles by the end of 2008, establishing a natural and a manufactured barrier over the heaviest illegal traffic areas from the Pacific Ocean to the Texas-New Mexico border.

© 2007 The New York Times