Police are stepping up counterterrorism measures in the city this week for the July 4th holiday following the unsuccessful terrorist activity in Britain over the weekend, Commissioner Raymond Kelly said yesterday.

Added checkpoints will be used to examine cars and trucks entering and leaving the city, while helicopters, boats, plainclothes officers, and radiological and chemical detectors will be deployed to monitor the more than 1 million people expected to gather in the city for the fireworks displays, Mr. Kelly said.

“We’ll have more resources available for the celebration of July 4th, but we’ve also upped our tempo, so to speak, since the events in the United Kingdom,” Mr. Kelly said. Still, the commissioner yesterday downplayed reports that Al Qaeda was planning a “spectacular” terrorist event in America this summer, echoing earlier statements by the Department of Homeland Security secretary, Michael Chertoff. “We have no specific information regarding a so-called spectacular event. This has been the sort of chatter out there for years, that Al Qaeda wants to do a spectacular event in the United States,” Mr. Kelly said. “To the best of my knowledge, there’s no specific information.”

Mr. Kelly said the police department was also seeking to combat drunk driving during the holiday by setting up more checkpoints around the city.