Democratic National Convention planners are running the drill again: ordering confetti, positioning lights, inviting delegates and preparing a political spectacle that will be seen nationwide when the pre-election party comes to Boston in July.

With event setup expected to take nearly 50 days, convention planners are already working long hours and slaving over checklists, just hoping to get the convention off the ground.

But unlike conventions past, planners face a new post-Sept. 11 organizational hurdle: preventing a mass-casualty terrorist attack from overshadowing the Democrats’ largest party of the year. From Secret Service infiltration to mandatory security checks at all MBTA subway stations, Bostonians may confuse the FleetCenter for Fort Knox.

“Our goal is to provide a safe and secure environment for everyone,” said Secret Service Agent Ann Romond. “An event of this size will cause inconveniences … and we will attempt to minimize disruption.”

But minimal disruption appears to be a relative term, and although many security measures will be invisible, the Secret Service has already announced that Green and Orange line trains will not stop at North Station subway platforms. Agents are also evaluating whether or not to close off North Station itself, causing hundreds of commuter rail and Amtrak trains to be diverted to temporary platforms away from the FleetCenter.

“The MBTA is still investigating plans to close North Station,” said MBTA Deputy Chief Police John Martino. “It is not simply a police decision, it is an overall safety decision.”

Martino said that if officials decide to close the station, any decision will be independent of the New York Metropolitan Transit Authority’s decision on whether to close Pennsylvania Station, which lies directly underneath the Madison Square Garden, home to the Republican National Convention. MTA officials are planning to keep the station open unless there is an imminent threat.

Even if North Station is closed, Orange Line trains will still run in their regular tunnel almost directly underneath the FleetCenter. T officials would not release tunnel blueprints but said the subway line runs between the new Central Artery tunnels and the FleetCenter.

MBTA and Secret Service officials would also not comment on funding or staffing issues and said they would only release security precautions that will directly impact the public.

Romond said that although the measures are not being made public, the Secret Service “will be prepared to handle a variety of potential situations at this event,” ranging from international or domestic terrorism to DNC protestors.

FleetCenter management would not disclose whether they would pay higher insurance rates for the arena during the event. Any increase could indicate an increased terrorist concern, according to Dave Desgupta, spokesman for the New York-based Insurances Services Organization, a group that evaluates high-profile buildings’ susceptibility to terrorist attacks and provides insurance estimates to insurance companies.

Desgupta said the ISO has estimated that Boston is the fifth likeliest city, based strictly on property-value-based evaluations, to be attacked by terrorists. Whether that factors into Secret Service initiatives in and around the FleetCenter remains undisclosed.

Romond said that in spite of the extensive security measures, officials could not guarantee the safety of the convention.

No security measures will be able to secure the event, Boston University professor of International Relations and former CIA agent Arthur Hulnick said.

“It will be as secure as human beings can make it,” he said. “It’s harder now [for terrorists to attack] than it was in 2001 because of all the security measures that have been put in place … but a suicide bomber can always get through and kill people.”