Heightened Alert

W A S H I N G T O N, May 21— Federal counterterrorism authorities called for increased security nationwide by raising the security alert to "high" but provided few specifics on where al Qaeda could strike inside the country.

Officials, fearful al Qaeda could expand its plans for a wave of attacks overseas into the United States, said they had nothing credible suggesting a time, location, method or target.

The decision to raise the national alert to orange, signifying a "high" risk of attacks, from yellow, meaning an "elevated" risk, came after a review of intelligence information by President Bush's homeland security council Tuesday, White House spokesman Ari Fleischer said. Orange is the second-highest on the five-color alert scale.

Plane Restrictions, SWAT Patrols

Around the country, state and local authorities stepped up security measures. Police in California worked 12-hour shifts. National Guard troops in New York were called up to protect subways and bridges. In Washington, the Capitol police SWAT team prepared to conduct random patrols.

The Federal Aviation Administration is planning to temporarily prohibit flights over sports stadiums and restrict small private planes flying within a 17.25-mile radius of the Washington Monument, said agency spokeswoman Laura Brown.

The FAA will also require private planes flying into three Washington-area airports — College Park, Potomac and Washington Executive/Hyde — to first land at Tipton Airport in Maryland so the pilots can be checked, Brown said.

Federal law enforcement officials said that among the intelligence picked up recently were two electronic transmissions that discussed the possibility of an attack on New York, Washington, Boston and more broadly the U.S. coastlines.

The officials, speaking on condition of anonymity, said there were doubts about the credibility of the threats and stressed that they were not the driving factors in the decision to raise the threat level.

Homeland Security Secretary Tom Ridge encouraged governors and mayors to deploy extra police and take other precautions, particularly at large public gatherings during Memorial Day weekend.