Authorities reviewing July 4 security after Marathon bombers were said to target iconic event

Authorities are carefully reviewing security measures for the July Fourth celebration in light of the deadly Boston Marathon bombings and disclosure that the suspects may initially have planned to target the Independence Day celebration.

The Boston Pops concert and fireworks display, summer highlights that draw an estimated 500,000 people, are among the host of upcoming public events, from college graduations to charity walks, that are prompting heightened security following the bombings.

State and local police officials would not say what specific measures might be put in place for July 4, but security specialists said they would probably include an increased police presence along the Charles River Esplanade, broader searches of bags and belongings, and tighter restrictions on movement during the event.

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They are also studying security plans at other large public events, such as the New Year’s Eve celebration in Times Square, to learn further ways to minimize threats.

Authorities expressed confidence that security — particularly since the Sept. 11, 2001, terrorist attacks — has been sound. But a spokesman for the State Police, which spearheads security at the July event, said officials are studying ways to make large public events “even harder targets for someone to attack.”

“The public should be assured that security measures include those that they see and others that they won’t see,” said David Procopio.

Governor Deval Patrick said Friday that the government would do “everything humanly possible” to make the concert safe, but called on the public to remain on alert.

“We’re going to do everything we can, everything humanly possible, to make it as safe as possible, and we have done so ever since security was first heightened after 9/11,” Patrick told reporters at Northeastern University’s graduation ceremonies. “It’s very important, at the same time, that people remain vigilant and be on a special level of vigilance in this coming year in the wake of the Marathon attacks.”

Northeastern’s commencement, held at the TD Garden, featured a strong police presence, including bomb-sniffing dogs. Guests were prohibited from bringing in large bags, and had their other bags checked upon entry.

For the Walk for Hunger on Sunday, organizers have asked the 35,000 participants not to bring large, bulky bags, and urged volunteers to look for unusual objects and suspicious behavior. More police will monitor the 20-mile route.

Ellen Parker — executive director of Project Bread, which holds the annual walk — said organizers decided to make the changes after consulting with police. After the bombings, fund-raising and registration slowed, and one school group pulled out of the event. Supporters wanted to know what plans were in place to make the race safe.

“If public safety told us that it wasn’t going to happen, then we were not going to do it,” she said. “But we were getting so many calls from people who said they wanted the walk to continue because the cause is so great.”

In Cambridge this week, police gathered to review security plans for Sunday’s MayFair, a Harvard Square festival that attracts about 7,000 people. Cambridge police also help cover several other events, including the Head of the Charles Regatta and the Cambridge Caribbean Carnival, that draw scores of spectators.

“Law enforcement is definitely looking at placing some type of access restrictions and security checks at most of these events,’’ said Deputy Superintendent Jack Albert. “There will also be additional police presence.”

In Boston, organizers of the city’s Caribbean Carnival in late August are also planning additional measures and are meeting with police later this month, far earlier than usual, to look for potential “gray areas” in security.

“We’ve worked closely with state troopers and Boston police over the years,’’ said Shirley Shillingford, president of the popular event. “We are looking at how we, as people in the neighborhood, can help them to do their job.”

Security specialists say large outdoor events like the July Fourth celebration are inherently vulnerable to attack, soft targets that cannot be made fully secure without changing the fundamental nature of the event.

“Whenever you have a crowd of people coming together, there’s a potential for bad things to happen,” said Henry Willis, director of the RAND Homeland Security and Defense Center.

At the same time, major events in a single location give authorities time to bolster security.

After the Marathon bombing, spectators may well be more attuned to their surroundings, making them more likely to notice suspicious behavior, specialists say. “You can protect each other,” Willis said.

Authorities echoed the call for vigilance.

“We do not want people to live in fear,” Procopio said. “All we ask is that they continue to be alert to anyone or anything that doesn’t look right and call 911 immediately if they do see something.”

Currently, spectators must pass through one of three entrances to the lawn in front of the Hatch Shell to have their bags checked. Alcoholic beverages, glass containers, large tarps, and any sharp objects are confiscated. After 6 p.m., admission is closed due to “crowds and public safety concerns,” according to the event website.

While bags are fully searched, there are no metal detectors.

Edward F. Davis, the Boston police commissioner, said Friday that after the Marathon bombings, authorities are renewing efforts to provide “the highest level of security possible.”

“We’re going to be there July Fourth to make people feel safe,” he said. “They should not be afraid to come into the city.”

As graduation season begins, colleges have also taken steps to bolster security, as Northeastern did Friday.

“I think in the current environment, it’s in everyone’s best interest to be careful,” said Ellen de Graffenreid, a spokeswoman for Brandeis University, which will have a heightened police presence at its May 19 ceremony.

Simmons College is asking attendees not to bring large bags and not to leave any belongings unattended.

“Public venues throughout the country are increasing security in light of these events; this should not be viewed as an indication of any increased threat to the Boston area,” the college said in its announcement.

Roger Cressey, security consultant and former White House counterterrorism adviser, said universities are doing their best to make guests feel safe, even if the actual threat is minimal.

“The message [colleges] must have is that we acknowledge this is a higher time of security awareness, and we are taking action,” Cressey said.