Police bomb squads responded to a firehouse in Brooklyn yesterday morning to examine a suspicious package during a weekend of heightened alert after an Israeli Web site reported that New York might be the target of a dirty bomb attack.

The threat turned out to be nothing, police officials said.

Nevertheless, the stepped-up police response turned into a fresh reminder of the usually invisible workings of the police department’s counterterrorism efforts, which have been greatly expanded in the years since the terrorist attacks of September 11, 2001.

On Friday, the Web site, Debka.com, which has links to Israeli intelligence, reported increased chatter on sites associated with Al Qaeda about a possible plot to detonate a radioactive bomb in major American cities including New York. Police then set up checkpoints around the city to monitor cars and trucks. Radiation detectors were also deployed, and scrutiny of the subway was increased. The Debka.com report had said Al Qaeda was threatening to hit New York City using trucks carrying radiological bombs.

“It is stressed that these deployments are strictly precautionary and not the result of any verified threat,” the police department said in a statement released Friday.

This summer, police have foiled a planned attack against a fuel pipeline leading to John F. Kennedy International Airport and a separate plan to attack Fort Dix in New Jersey.

In the wake of those plots and plots discovered in Britain, experts have warned that New Yorkers should be more concerned about attacks by groups that are less sophisticated than Al Qaeda. Some officials characterized the airport plot as amateur.

Even after police determined that the dirty bomb threat was unfounded, some New Yorkers noticed an increased police presence around the city.

Yesterday, a special police unit responded to a call of a suspicious package outside the , Ladder 176/ Engine 233 on Rockaway Avenue in Brownsville. After checking the package with a bomb meter, police determined it was innocuous.