President Bush cautioned Tuesday that the foiled plot in Britain to blow up jetliners over the Atlantic Ocean means the U.S. will be fighting terrorists for years to come.

"America is safer than it has been, yet it is not yet safe," Bush told reporters in an operations center at the National Counterterrorism Center in McLean, Va., just outside Washington.

Bush thanked the people who are involved in counterterrorism, and credited their help in last week's arrests of more than two dozen people in England and Pakistan in what officials say was a plot to blow up as many as 10 passenger planes between Britain and the United States.

He said their work takes "an incredible amount of time, energy and effort."

Bush said that plot is indicative of the challenges that America faces from terrorists now and for years to come.

"I will assure the American people that we are doing everything in our power to protect you," Bush said in brief remarks to reporters. He spoke as police in London, meanwhile, announced another arrest in the alleged London airliner bomb plot.

At the center where employees watched large screen monitors and surveyed electronic maps of various parts of the world, Bush attended a National Security Council and Homeland Security Council briefing and a meeting with the counterterrorism team.

The nation's safety looms large as an issue in the midterm elections less than three months before the Nov. 7 contest. Both Republicans and Democrats are maneuvering for the political advantage in an election where control of Congress is at stake.

On his handling of foreign policy and terrorism, Bush was at 40 percent approval in an early August AP-Ipsos poll. That's near his all-time low of 39 percent on those issues in AP-Ipsos polling.

There have been mixed signals since the terror plot was foiled on whether his approval is rising in these areas. In some polls, there have been some signs of improvement, while other polls show no change.