WASHINGTON (AP) - Facing stiff opposition from two Western states, the Pentagon on Thursday scrapped plans for a 700-ton non-nuclear test blast that would have produced the first mushroom cloud of dust over the Nevada desert in decades.

The Defense Department said it would find other ways to test the nation's ability to penetrate underground bunkers that produce and store weapons of mass destruction.

The cloud may have reached an altitude of 10,000 feet over the site about 90 miles northwest of Las Vegas, an eerie echo of long-ago open-air nuclear testing.

Originally scheduled for last June 2, the test blast - called Divine Strake - had been postponed indefinitely until the Defense Threat Reduction Agency finally canceled it.

"I have become convinced that it's time to look at alternative methods that obviate the need for this type of large-scale test,'' he said in a statement.

The decision was not based on any technical information that indicated the test would harm workers, the public or the environment, according to James Tegnelia, director of the Pentagon unit that works on technical aspects of how to destroy deeply buried enemy weapons.

It was in March 2006 that he had likened the spectacle of a test explosion to a mushroom cloud.

"I don't want to sound glib here, but it is the first time in Nevada that you'll see a mushroom cloud over Las Vegas since we stopped testing nuclear weapons,'' Tegnelia said at the time to reporters.

The United States stopped conducting aboveground nuclear tests in 1963.

In Nevada and Utah, there was concern that the blast would scatter decades-old radioactive material from previous Cold War-era tests. Other critics contended the explosion would mark a step toward new tests to develop "bunker buster'' nuclear weapons.

Two months ago, the agency released a new environmental report that confirmed there is radioactive material about a mile from the blast site. Officials insisted any harm would be "extremely unlikely.''

The agency said in a statement it would develop other ways to gather the kind of data that Divine Strake would have provided. "Such methods to assess capabilities to defeat underground facilities do not currently exist,'' it said.

The agency is committed "to help develop non-nuclear means to defeat underground targets. I am optimistic that we will succeed,'' Tegnelia said.

Senate Majority Leader Harry Reid, D-Nev., and other lawmakers said they understood the need for tests to develop defense strategies.

But, Reid said, "there were still many questions left unanswered, including the possible environmental effects.''

The loudest critics said the plan revived bitter memories of government "lies'' during Cold War-era tests, when officials said there would be no danger.

Thousands of people who lived near the Nevada Test Site - called downwinders - were exposed to cancer-causing radiation from weapons tests.

Residents feared Divine Strake would spread more radioactive material or lead to further nuclear experiments there.

"If this announcement truly signals the end of Divine Strake, my hope is that DTRA would instead spend time and money on developing a conventional weapon that would actually be useful to our military in destroying deeply buried terrorist targets,'' said Rep. Jim Matheson, D-Utah.

John Wells, a Las Vegas carpenter and regional representative to the Western Shoshone National Council, said the blast would "compound wrongs'' for the American Indian tribe.

The tribe fought the test in court and long has contested the government over the test site, now contaminated from years of nuclear tests.