The evacuation of a section of John F. Kennedy International Airport after the discovery of a suspicious package set an already jittery New York on edge yesterday as Britain reacted to two terrorist plots over the weekend.

Security was tight for a second day at city airports after a sport utility vehicle rammed into the Glasgow airport on Saturday in the latest of a series of amateur plots in America and Europe. On Friday, British authorities discovered two cars in London that held explosive devices that had failed to detonate.

Cars were sent through checkpoints before approaching the terminals at New York area airports, and police maintained their heightened presence in subways and around the city’s bridges, tunnels, and tourist attractions.

British authorities suggested yesterday that the two plots in London and Glasgow were linked to each other, and to the terrorist group Al Qaeda. But American officials suggested that the recent plots, including a foiled plan to bomb a fuel line leading to JFK airport and another to attack Fort Dix, were something new. “What we’re seeing with terrorism is a change,” Senator Schumer said yesterday. “They are home-grown groups not really connected to Al Qaeda.”

The former deputy commissioner of counterterrorism for the New York City Police Department, Michael Sheehan, said the smaller, improvised plots present a different challenge to law enforcement and intelligence agencies.

Of the homegrown plots, he said: “Those are very hard to find. That’s the bad news. The good news is that they’re not very sophisticated.”

A senior fellow at the Manhattan Institute, Timothy Connors, said that in response, the government should divert resources to nimbler local police forces.

At JFK yesterday, the suspicious package found on a curb outside Terminal 9 turned out to be a case full of cologne, a Port Authority spokesman, Steven Coleman, said. After the brief evacuation, airport workers and airline passengers said they were trying not to let fear interfere with their day.

“As I was coming in, I saw police officers all over, so I knew it would be that kind of day,” an operational coordinator at JFK, Rachel Domingue, 35, said. “If I thought it about it, I wouldn’t even be able to show here.”

A traveler from California on her way to France via London, Lia Usilton, 19, said she would not change her vacation plans, despite the elevated threat levels in Britain. “I think it’s definitely a concern,” she said. “But you can’t swim across the Atlantic.”