(Adds detail on stadium security measures, comment from security expert)
By Scott Malone
NEW YORK, Jan 29 (Reuters) - Bomb attacks of the kind that tore through mass transit sites in Russia ahead of the upcoming Sochi Olympics are a top concern of security officials preparing for Sunday's Super Bowl, the head of the New Jersey State Police said on Wednesday.
While law enforcement officials said they were not aware of any specific threats targeting the Feb. 2 National Football League championship in East Rutherford, New Jersey, attacks like those that killed 34 people in two days in Russia late last year are their biggest worry.
"Of particular concern to us is what was going on overseas in Volgograd in regard to the Sochi Olympics. As you know both of those bombings were targeting mass transit," Rick Fuentes, superintendent of the New Jersey State Police, told reporters. "That is a concern with the mass transit; we've prepared ourselves for it."
Officials have sharply limited parking at MetLife Stadium, where Sunday's game will be played, and expect as many as 30,000 people to arrive by bus or rail. Security screening will start at train stations, where fans will not be able to board stadium-bound trains or buses without tickets to the game, officials said.
New York Police Department Commissioner William Bratton said that while authorities were focused on a mass transit type of attack, they were not aware of any specific plans to target the game or surrounding events.
"We are keeping an eye on activities around the world, but certainly at this time there are no threats directed at this event that we're aware of," Bratton said.
The stadium is located about 10 miles (16 km) west of New York City, the site of the Sept. 11, 2001, attacks. It has been locked down all week, and authorities are scanning all vehicles that go in, a practice that will continue on game day, officials said.
Bratton noted that New York police were using extensive intelligence-gathering operations developed since the World Trade Center attack to watch for possible threats.
About 400,000 people are estimated to have traveled into the region for events surrounding the game, though only about 80,000 fans will get to see the Seattle Seahawks-Denver Broncos match-up in person.
Some 4,000 security officers will be on hand for Sunday's game, and fans will be prohibited from bringing bags into the stadium unless they are transparent and no larger than 12 inches by 6 inches by 12 inches (30 cm by 15 cm by 30 cm), with women's purses limited to 4.5 inches by 6.5 inches (11.4 cm by 16.5 cm).
Stadium gates will open at 2 p.m. on Sunday, more than four hours before kickoff, to allow fans to pass through a security cordon that will include metal detectors and pat-downs of fans bundled up for temperatures that could drop to 29 degrees Fahrenheit (minus-2 Celsius).
At an undisclosed location near the stadium, officials from some 100 security agencies are monitoring feeds related to security concerns 24 hours a day, Fuentes said.
The contained nature of the game makes it easier to secure than public events such as the Boston Marathon, where two pressure-cooker bombs were detonated amid a finish line crowd of thousands of spectators, volunteers and athletes on April 15, killing three people and injuring 264.
The "Super Bowl Boulevard" street fair, along a 3/4-mile (1.2 km) stretch of New York's Broadway, presents a different challenge, as it will be wide open, with up to 1 million people expected to visit attractions, including the Super Bowl trophy and a towering toboggan run.
Large numbers of police officers have been assigned to the event and organizers have taken steps such as removing trash bins along the route and replacing them with clear plastic bags that can be easily inspected visually. Large numbers of security cameras and plainclothes police officers will be deployed along the area, although officials would not disclose precise details.
In planning for the event, Bratton said New York police had prepared to respond to a variety of attacks.
"There was a lot of focus on the lone wolf, the 'backpack left unsecured' scenarios, so we're prepared," Bratton said.
The Boston bombers left their homemade explosives along the course in black backpacks.
Fans who visited the street fair on Wednesday said they were confident due to the large police presence.
"I can see cops all over, so I feel like it's pretty safe," said Steven Ferraro, 18, of New York's Brooklyn borough. "Anything can happen anywhere, but I think it's safe."
Security experts, however, note that it is all but impossible to secure open-air events entirely.
"No amount of technology or deployment of resources and 21st century technology is going to guarantee under all circumstances that something terrible cannot happen," said Tom Nolan, chairman of the criminal justice department at the State University of New York in Plattsburgh. "You have to accept some degree of risk and you have to accept a new level of intrusion into your privacy." (Additional reporting by David Jones in East Rutherford, New Jersey; Editing by Cynthia Johnston, Tom Brown and Dan Grebler)