WASHINGTON — In an aggressive move to finish building 670 miles of border fence by the end of 2008, the Department of Homeland Security announced yesterday that it would waive federal environmental laws to meet that goal.

The two waivers, allowing the department to slash through a thicket of environmental and cultural laws, would be the most expansive to date, encompassing land in California, New Mexico, Arizona, and Texas that stretches about 470 miles.

The waivers are unfavorable with environmentalists and border communities, which see them as a federal imposition that could damage the land and disrupt wildlife. But they are praised by conservatives who championed the 2006 Secure Fence Act, despite the reluctance of President Bush, who has said a broader approach is needed to deal with illegal immigration.

Republicans greeted the news with satisfaction.

“It’s great. This is the priority area where most of the illegal activity is going on and where most of the deaths are occurring,” the chairman of the Immigration Reform Caucus, Rep. Brian Bilbray, a Republican of California, said.

Wildlife groups reacted with dismay. An attorney with Defenders of Wildlife, Brian Segee, said, “It’s dangerous, it’s arrogant, it’s going to have pronounced environmental impacts and it won’t do a thing to address the problems of undocumented immigrants or address border security problems. It’s an incredibly simplistic and ineffective approach to complex problems.”