BILLINGS, Mont. — Mining claims for copper, uranium and other metals are being staked near growing towns and cities across the West at an accelerating rate, according to a new report that casts the trend against the industry's legacy of environmental pollution.

The Pew Campaign for Responsible Mining and the Environmental Working Group said in a report released Tuesday that active mining claims on federal land near Western cities and towns increased almost 50 percent since 2003, to more than 50,000 claims.

The claims range from stakes for gold in California and copper in Arizona to uranium in Wyoming and platinum in Montana. Developed areas with the highest number of claims within five miles include Las Vegas, Nev., and Phoenix, with more than 5,000 each; La Sal, Utah, with 3,000; and Tucson, Ariz., and Riverside-San Bernardino, Calif., with about 1,700 each.

"These claims are increasingly encroaching on places where people live, and there's not much you can do under the existing law to stop that," said Environmental Working Group analyst Dusty Horwitt. "It only takes a small percentage of claims to be developed into mines to cause a huge problem."

The National Mining Association says the increase in claims is driven by a surging worldwide demand for raw materials. The association's Luke Popovich said 5 percent or less of claims are actually mined and added the industry is working to lessen the amount of pollution it creates.

Tuesday's report, Popovich said, shows environmentalists are "against those communities that depend on mines for their livelihood."

The federal government reported last month that the metal mining industry disposed of or released 1.2 billion tons of toxic chemicals in 2006 — more than any other industry.

The environmental groups' report comes as Congress grapples with proposed sweeping changes to the 1872 Mining Law. That law has come under scrutiny in recent months for its lax environmental protections and for allowing companies to pay only a nominal price to mine on public land.

The House last year passed a broad overhaul of the law — a bill supported by environmentalists and opposed by industry. The Senate is set to hold the third in a string of hearings on the issue today before the Energy and Natural Resources Committee.