"Credible reporting now indicates that al-Qaida is moving forward with its plans to carry out a large scale attack in the United States in an effort to disrupt our democratic process," he said.

Mr. Ridge said U.S. officials do not have specific information about where or when the attack might occur, but he did mention the upcoming political conventions that include the Democrats gathering in Boston at the end of this month and the Republicans holding their convention in New York in late August.

Mr. Ridge also said the recent arrest of terrorism suspects in Britain, Jordan and Italy yielded new information about possible terror plots.

"What we are alluding to there is not only did they have individuals in place, but they had the means to the end that were part of the plot," he added. "They had the people ready to operate and they had munitions and the ability to conduct the terrorist attack. That was all part of the apprehension."

Members of Congress were given a private briefing about the terrorism threat. Among them was the Senate Republican Majority Leader, Bill Frist of Tennessee.

"There is obviously no reason for panic or no reason for paralysis. But the fact that general intelligence says that the country is at some increased risk between now and the time of the presidential election, it is important for people to be aware of that," he noted.

Tom Ridge said the government is not raising the terror alert level, which now stands at elevated. He also said law enforcement agencies across the country are better prepared to deal with this latest threat than they were even a year ago.

"This is unprecedented communication and cooperation at the national, state and local levels," he said. "This new ability to receive and distribute critical information allows us to make better decisions more quickly and take action that would deter, detect and diffuse terrorist attacks."