In the wake of a foiled terror plot that may have targeted Pier 39, the San Francisco Police Department is putting more officers on the street for New Year’s Eve, when large crowds will gather around the city to watch fireworks, drink Champagne and ring in 2018.

A Modesto man was arrested Dec. 20 for what the FBI said was a planned Christmas terror attack inspired by the Islamic State, possibly targeting Pier 39. Days later, Police Chief William Scott said the department’s plan for public safety at New Year’s Eve celebrations remains mostly the same — with added backup.

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“Not so much significant changes (to the plan), but there will be additional deployment,” Scott said, at a news conference Friday with acting Mayor London Breed and Fire Chief Joanne Hayes-White. A spokesman for the Police Department declined to say how many additional officers would be deployed. Scott emphasized the collaboration between San Francisco police and other local, state and federal agencies, including the FBI.

“We want the public to know that there are no credible threats,” he said.

Still, he said there would be a heavy police and law enforcement presence all over the city.

“There will also be a very visible presence along the wharf area at Pier 39,” he said, citing the recent arrest. “There will also be officers out there that you won’t see, because we will have a plainclothes presence there as well.” There will be no discretionary time off for officers on New Year’s Eve, Scott said.

There were several deadly terror attacks in 2017 and other reminders of the nightmare scenarios that can occur in large crowds. On Oct. 1, for example, a man fired repeatedly into a concert in Las Vegas, killing 58 people and injuring hundreds of others. On Halloween, another man drove a truck down a bicycle path in New York City, killing eight people.

Scott declined to discuss specific plans for different types of attacks, citing tactical reasons for keeping them secret. Other police departments, including those in Las Vegas and New York City, have said they are adding countersnipers to their deployment this year.

Terror attacks are only one of the threats officials are preparing to address. Breed, Hayes-White and Scott all admonished citizens not to drive drunk. Muni and Caltrain will be free to all in San Francisco starting at 8 p.m. on New Year’s Eve in hopes of keeping partygoers from getting behind the wheel. There will also be additional late-night service on Muni, BART and Caltrain.

“I do like to underscore the fact that there are really no excuses for drinking and driving any night of the year, particularly New Year’s Eve,” Hayes-White said.

Breed also reminded the public that shooting off fireworks is both illegal and dangerous.

“If you want to see fireworks, go to the show,” Hayes-White said. The San Francisco Fire Department will have dedicated resources monitoring illegal fireworks.

Despite the concerns that come with New Year’s celebrations, Scott emphasized that San Francisco residents and visitors should be able to ring in 2018 in the city — safely.

“Our public needs to be able to do the things they want to do freely,” Scott said. “When we have a terrorist event or threat of a terrorist event, and then we start changing our behavior ... we stop doing things that we as Americans or residents of this nation that we have a right to do, then we’re in the wrong place.”

Sophie Haigney is a San Francisco Chronicle staff writer. Email: sophie.haigney@sfchronicle.com Twitter: @SophieHaigney