NEW YORK — Revelers can expect hovering helicopters and bomb-sniffing dogs with their champagne and confetti as cities hunker down for their most heavily guarded New Year's Eve in memory.

From Times Square to the Las Vegas Strip and California's Rose Parade, police were rolling out unprecedented security measures triggered by a hike in the national terrorism alert to orange, its second-highest level.

In New York, workers sealed manhole covers and removed mailboxes to guard against any potential bomb attack in Times Square. More than 750,000 revelers were expected to gather under the guard of counter-sniper teams and seven police helicopters.

Armed helicopters were also to prowl the Las Vegas Strip, where 300,000 people were anticipated.

In New York, Mayor Michael Bloomberg said the city was well-protected. "Sadly, terrorism is something that we have to live with," he said. "Leave the worrying to the professionals."

New York police were focusing more heavily than last year on hotels, landmarks and ferry terminals as a result of their analysis of anti-American "chatter" culled from the Internet and other sources, police Commissioner Ray Kelly said.

"We think it's prudent for us to do that," he said.

Partygoers headed to New York were warned to expect long delays at bridges and tunnels. Every vehicle on affected routes is subject to a random stop and search, New Jersey officials said. State troopers will be riding the rails to assist transit police on trains going in and out of New York.

Officials nationwide said there were no specific threats to traditional gatherings and urged people to go forward with celebrations.

Still, FBI and other federal agents have been sweeping the Las Vegas area for weapons or threats, said Ellen Knowlton, FBI special agent in charge in Las Vegas.

The Strip has 74,344 hotel rooms and 18 of the nation's 20 largest hotels.

Nearly the entire Las Vegas police force of about 2,000 officers was to be on duty, plus about 600 jail officers. Authorities also were relying on help from about 4,000 hotel security guards.

On Monday, the U.S. Department of Homeland Security and the Transportation Security Administration said airspace over the Strip would be restricted.

Thousands of local officers and federal agents were to fan out through Pasadena, Calif., where revelers gather along the 5 1/2-mile Rose Parade route and attend the Rose Bowl football game. Video surveillance cameras were to capture images of spectators lining the streets.

Flights over the Rose Bowl were to be limited to police and military aircraft; everyone working in the stadium, from hot dog vendors to television camera crews, was being required to wear photo ID.

Still, terrorism concerns did not dim the enjoyment of visitors Tuesday.

"We decided not to live our lives in fear, and do what we want to do," said Janet Powles, 60, of Rapid City, S.D., as she watched volunteers apply flower petals to floats in the Rose Palace.

The increase in the alert level to orange and reports of threats to Las Vegas did appear to affect business there. Deutsche Bank analyst Marc Falcone said New Year's Eve cancellations jumped in the last week. His survey of Las Vegas hotels found twice as many cancellations this year as in 2002.

Boston was expecting more than a million visitors for its "First Night" arts festival, the nation's oldest such celebration. Security there was to remain consistent with the last two years' events.

Metal trash cans are removed from the Boylston Street parade route and replaced with cardboard boxes, to minimize damage if there is an explosion. And the Massachusetts Bay Transportation Authority was posting security officers and bomb-sniffing dogs on buses, subways and trains carrying revelers into the city.

In smaller cities and rural areas, officials described increased security at public places such as malls and heightened surveillance at vital infrastructure such as bridges, power plants, water systems, airports and ports.

Associated Press Writer Ken Ritter in Las Vegas contributed to this report.