Police will resume inspections of bags on public trains, buses and boats in the greater Boston area for the first time since the city hosted the Democratic National Convention in 2004, Massachusetts Gov. Mitt Romney announced Thursday.

Romney, a Republican weighing a 2008 run for president, said that the inspections for possible explosives were not a response to any immediate threat, but that police recognize transportation systems are vulnerable to terrorist attacks.

"We are facing a very different threat. We need a very different tactic," the governor said.

Daniel Grabauskas, general manager of the Massachusetts Bay Transportation Authority, said the inspections would begin as early as next week and could be done quickly enough to guarantee riders are not slowed down. Police will check a bag by swabbing the outside for any traces of explosive materials, a minute-long process that can be followed by a request to open the bag.

To guard against ethnic profiling, police will either inspect all riders entering a station or pick out riders on a random numerical basis — every third, or fifth or eighth rider, Transit Police Chief Joseph Carter said.

The transit system is also adding uniformed teams of officers trained to try to pick out potential terrorists based on their behavior.

The area transit agency became the nation's first to randomly inspect bags and packages on subway and commuter trains in 2004 when Democrats held the first national political convention after the terrorist attacks of Sept. 11, 2001.

Fears of terrorism prompted extraordinary security measures including sealing off the area around the convention site. Civil liberties groups complained that the bag inspections violated constitutional protections against unreasonable searches. The inspections ended after the convention was over.

Concern over subway terrorism increased after four bombers attacked London's underground system last year, killing 52 people and themselves.

Boston's move also comes two months after a federal appeals court ruled that random bag searches on New York subways are constitutional, saying they are an effective and minimally invasive way to help protect a prime terror target. Searches on the New York subway system began after the London bombings.