WASHINGTON -- A government official's comment that a 700-ton blast scheduled June 2 at the Nevada Test Site would send a "mushroom cloud over Las Vegas" set off a firestorm on Thursday even though state officials signed off on the experiment in January.

Talking to reporters at the Pentagon, James Tegnelia, chief of the Defense Threat Reduction Agency, said, "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 the test, called "Divine Strake," is part of an effort to develop weapons that can destroy underground bunkers storing nuclear, chemical or biological weapons.

Calls and e-mails to the agency were not returned on Thursday. It was established in 1998 as a branch of the Department of Defense to reduce the threat to the United States and its allies from weapons of mass destruction.

The mushroom cloud image disturbed Rep. Shelley Berkley, D-Nev. She took to the House floor to sharply criticize Tegnelia for his comments.

"It's bad enough that we didn't get prior notice and ... obviously, the congressional delegation wasn't briefed, but the people of the state of Nevada haven't been briefed either," Berkley said.

As it turned out, Berkley and the other four members of the congressional delegation were notified about the planned explosion in a Dec. 19, 2005, letter from the National Nuclear Security Administration.

In addition, Nevada Department of Administration official Zosia Targosz said in a Jan. 9 letter to the NNSA's office in Las Vegas that "your proposal is not in conflict with state plans, goals or objectives."

Berkley spokesman David Cherry acknowledged Berkley was notified last year about the blast.

"But the notification did not include phrases like 'mushroom cloud over Las Vegas,' " Cherry said.

Sen. Harry Reid, D-Nev., issued a statement calling Tegnelia's comments "irresponsible and inflammatory." Reid said he would press for a briefing from military officials.

Sen. John Ensign, R-Nev., was traveling and could not be reached for comment. His spokesman, Jack Finn, said Ensign's staff have contacted officials at the test site and the Defense Threat Reduction Agency.

Reps. Jim Gibbons and Jon Porter, both R-Nev., issued statements saying a report in November indicated there would not be a safety risk or adverse environmental impact from the test. They added they will continue to monitor the situation but raised no objection to the proposed explosion.

Tegnelia said the Russians have been told about the test.

Darwin Morgan, an NNSA spokesman at the test site, said the detonation will occur in a pristine area about 90 miles northwest of Las Vegas.

The 700 tons of ammonium nitrate fuel oil will be poured into a 30-foot pit that will be dug above one of the test site's tunnels, Morgan said.

Berkley said Tegnelia told her the mushroom cloud that results from the blast will be visible from Las Vegas.

But while he acknowledged there will be a mushroom cloud, Morgan said surrounding mountains are likely to block the view from Las Vegas.

Morgan also said it is "highly unlikely" the blast will be felt in Las Vegas.

"The most likely scenario is that someone in Indian Springs might hear something that sounds like distant thunder," Morgan said.

Morgan described the blast as "an open-air experiment."

"The test site is a user facility for the national labs and the Defense Department and the Defense Threat Reduction Agency. This is what we do -- high hazard operations."

The 700-ton blast will not be the largest ever conventional test in Nevada, according to Morgan. In 1993, a 2.9 million-pound explosion occurred in a test site tunnel.

The last nuclear test at the test site occurred Sept. 23, 1992.

Frank von Hippel, a Princeton University professor who served as an assistant director for national security during the Clinton administration, said the June test sounds similar to the Bush administration's abandoned plan to develop a nuclear bunker buster.

"If this is really being done to simulate a conventional weapon, I don't understand why they aren't using 20 tons (of explosives) instead of 700 tons," von Hippel said.