Mayor Bloomberg was at 35,000 feet on his way home from the International Olympic Committee meeting in Singapore yesterday when he learned of the terrorist attacks in London.

It was more than four hours before the start of the business day in New York City, but the mayor immediately consulted with officials on the ground in New York City to determine what the city would do to guard against attacks here.

The police commissioner, Raymond Kelly, ordered officers who had reported to work at midnight not to go home at 8 a.m. Instead they were deployed at transportation hubs and other vulnerable areas around the city. Other officers, including some from the bomb squad, were ordered into uniform and deployed around the city.

At about the same time, Governor Pataki was on the phone with the Homeland Security secretary Michael Chertoff, who informed the governor that he was raising the nation’s mass transit systems to “level orange” on the country’s security alert system. New York’s alert level has been at no less than “orange” since the attacks of September 11, 2001, but the governor took steps to ratchet up security.

By rush hour, the police presence in New York City had approximately doubled on buses, subways, bridges, and tunnels, and by 12:30 p.m. Mr. Bloomberg joined Mr. Pataki and other officials at Grand Central Terminal and stood before two dozen television cameras to discuss the city’s precautionary measures.

“I think what you’re seeing is the kind of cooperation and coordination that everybody needs if we are going to keep this city, this country, and this state safe,” the mayor said. “You see it at the level of the state and the city. You see it at the level of all of the different police departments involved. You see it at the level of the police and the other agencies that have to be ready and are part of our surveillance, our preparation, and our deterrence.

“This morning,” he continued, “as soon as the attack was learned about, the NYPD responded by implementing additional counterterrorism measures to protect New York’s transit system and secure our city.”

Though there were no recent credible terrorist threats against New York or America, the officials said, Messrs. Bloomberg, Kelly, and Pataki detailed a long list of precautionary measures that would remain in place indefinitely. They included deploying a police officer on each subway train, conducting sweeps of each subway car, placing plainclothes officers on the subways, deploying heavily armed Hercules units, patrolling the skies over the city with helicopters, diverting all truck traffic from the Williamsburg Bridge to the Manhattan Bridge, and sending more bomb-sniffing dogs to the streets and the transit hubs.

The Police Department also activated its Emergency Operation Center to facilitate face-to-face coordination between city and state agencies. Mr. Pataki signed an executive order that gave police officers in New Jersey and Connecticut full police power on the trains into and out of New York.

The governor’s senior adviser on counterterrorism, James Kallstrom, used the press conference at Grand Central to complain about the quantity of the nation’s Homeland Security funds sent to New York.

“This should be a reminder as we watch the carnage, as we watch the people being medevaced from these sites, we are still fighting a global menace that still has reach, still has power,” he said. “This should be a wakeup call to the national command in Washington that we need to do more to protect this great country and our way of life. I would encourage people in Washington to think again about how Homeland Security funds are deployed, how they go towards preventing the next attack here in the United States.”

Mr. Kallstrom, a former assistant director of the FBI, continued: “We need to put federal money into communications. We need to talk about the lack of frequency spectrums, and all these issues that really haven’t had much movement since 9/11.”

When the press conference wrapped up, Messrs. Bloomberg and Pataki boarded a subway train to ride downtown together.

Meanwhile, the Democratic mayoral candidates canceled political events they had planned for yesterday morning, citing the terror attacks in London. But by the afternoon, most of the campaigns had sent statements to the press.

The borough president of Manhattan, C. Virginia Fields, issued a list of seven recommendations for making the city’s subway riders safer. They included placing Metropolitan Transportation Authority workers in subway station booths, providing emergency instructions in multiple languages, equipping tunnels and stations with cell-phone reception, and expanding the use of security cameras in stations.

A congressman from Brooklyn and Queens, Anthony Weiner, said in a statement: “Today is a day that reminds us all here of an important truth. Despite all the politics and arguments – what unites us is much stronger than what divides us.”

The City Council speaker, Gifford Miller, said in a statement: “The horrific terrorist attacks on London today remind us that we have to remain vigilant in protecting New York, and strengthen our city’s resolve to not live in fear.”