(CBS) The federal government said Tuesday that pilots will not be allowed to have guns in the cockpits of commercial airplanes.

The announcement was made at a Senate Commerce Committee hearing by John Magaw, undersecretary for transportation security. It followed months of debate over whether arming pilots would be a deterrent to hijackers.

Both Transportation Secretary Norman Y. Mineta and Homeland Security Director Tom Ridge previously indicated their opposition to arming pilots.

Magaw gave no reason for his decision, which was announced in response to a question from Arizona Sen. John McCain, the top Republican on the committee.

Magaw said a formal announcement will be made later in the week.

The decision to forbid guns to pilots was the latest development in the war on terror. Attention has been focused on what the government may have known about the possibility of a major terrorist attack prior to Sept. 11.

The Justice Department is taking issue with a report published Tuesday that Attorney General John Ashcroft and FBI Director Robert Mueller were told about a memo from an FBI agent in Phoenix expressing concern about a large number of Arabs training at a U.S. flight school a few days after the Sept. 11 attacks.

Citing government officials, the New York Times reported that neither official briefed President Bush about the memo until recently.

Ashcroft and Mueller have not said publicly when they learned of the July 10 memorandum, the Times said.

"But the officials (interviewed) said that within days of the attacks, senior law enforcement officials grasped the document's significance as a potentially important missed signal," the report added.

But CBS News Correspondent Stephanie Lambidakis reports that a Justice Department spokesman said "neither John Ashcroft or Bob Mueller have a recollection of being briefed on the Williams memo" several days after the attacks. "They (the AG and FBI chief) were beyond that in the investigation … everyone was pretty aware there were pilots who had trained at flight schools. They were frantically checking the flight schools.

"Ashcroft did not have a specific briefing on the memo until 3-4 weeks ago... about a month ago."

In recent days, the Bush administration has been more blunt than ever about terrorist threats. Mueller said Monday that suicide bombers who walk into public places carrying explosives will eventually strike in the U.S. Vice President Cheney said over the weekend another attack is a matter of when, not if.

"There will be another terrorist attack. We will not be able to stop it," Mueller told a group of local prosecutors meeting in suburban Alexandria, Va. "It's something we all live with."

Mueller's sobering predictions — "I wish I could be more optimistic" — came one day after Cheney said it was almost a certainty the United States would be attacked again by terrorists.

And while shopping malls, apartment complexes and public buildings have all been mentioned as potential targets, one U.S. official told CBS News the administration's greatest fears still center around commercial aviation, specifically the possibility a suicide bomber would check a suitcase with a bomb aboard a domestic flight.

CBS News Correspondent Jim Stewart reports airlines are rushing to obey a congressional order that they inspect all baggage - both hand-carried and checked - but are not expected to fully comply until the end of the year.

Officials described the latest threat warning as a product of "communications intercepts" including "Internet chatter," "hard intelligence retrieved from Afghanistan" and the "results of prisoner interrogations."

The latest intelligence shows a marked increase in activity by Osama bin Laden's al Qaeda network over the past few weeks, suggesting new attacks may again be in the offing, said a senior U.S. official, speaking on condition of anonymity.

Defense Department spokeswoman Victoria Clarke stressed that despite major successes against al Qaeda in Afghanistan, where a U.S.-led military campaign has destroyed the group's main camps, it and other groups remained a threat.

"We have always said this is about more than one person, one network and certainly is about more than Afghanistan," Clarke said.

Islamic groups like Hezbollah and Egypt's Islamic Jihad could be planning to attack the United States and may be more able to do so than al Qaeda, top lawmakers said.

Neither group has been linked directly to activities on U.S. soil, and such an attack would represent a major change in their tactics.

Mueller said the difficulty of getting informants inside terrorist groups targeting the United States makes it much harder to obtain advance information.

Cheney said Sunday he sees "a real possibility" that suicide bombers may hit the United States if those who have attacked Israel succeed in changing the situation in the Middle East.

"Terrorism is an evil, pernicious thing, and it is one of the biggest challenges we've ever faced as a nation," Cheney said.

The Bush administration, meanwhile, is fighting Democratic-led efforts to have an independent commission rather than existing congressional intelligence committees study its performance before Sept. 11.

Calling for a commission, House Minority Leader Richard Gephardt, D-Mo., said various branches of government possessed information last summer about the Sept. 11 terrorists.

"Unfortunately, these and perhaps other documents were not compiled in a manner that enabled our counter-terrorism experts to use them most effectively," he said.

The White House has pledged to co-operate with a joint investigation of the House and Senate intelligence committees. But Cheney warned over the weekend over making sensitive information public. The committees want more cooperation by the FBI and CIA on sensitive information. Committee members say the inquiry will be "worthless" unless the agencies are more forthcoming.