Employees at the law firm of Prince, Lobel, Glovsky & Tye like to climb to the roof on sunny days to take in some fresh air or views of the city's historic waterfront or downtown skyline. But its location just a few blocks from the FleetCenter, site of Democratic National Convention (search) in five weeks, is causing some angst.

Managers have hired a security guard to patrol the building in case protests become destructive. They're also wondering how their 90 employees will get to and from work when about 40 miles of roads will be closed that week.

"It's going to be a pain in the neck," said managing partner Bob Maloney.

Major events here usually meet with applause from local companies, shopkeepers and restaurateurs excited by the prospect of increased business from out-of-towners. But the inevitable traffic tie-ups and other disruptions expected for the July 26-29 convention have left many asking whether the costs will outweigh the benefits.

Gillette Co. is telling workers to head for home an hour earlier than usual and is stocking up on food for the staff in case deliveries don't make it. Brown & Brown's accountants will work from client offices instead of at the firm, just a block from the FleetCenter.

Big employers — from Liberty Mutual Group to John Hancock Financial Services — have made emergency plans in case of major disruptions in Boston, which is playing host to its first major national political convention.

Mayor Thomas Menino has urged companies to encourage employees to car pool and use public transportation to ease the backups on the city's notoriously jumbled downtown traffic grid and narrow streets. He also wants them to accommodate workers wishing to take off the week, work from home or stagger their hours and commuting times.

Major highways to and from the city will be closed during the convention and some commuter trains will stop miles outside the city, with passengers cramming aboard shuttle buses for the ride downtown. The FleetCenter sits atop a major commuter-rail hub that will be closed convention week, as will a city subway stop there.

The convention is also the first since the terrorist attacks of Sept. 11, 2001, bringing with it heightened concern about another assault. The two airliners that crashed into New York's World Trade Center took off from Boston's Logan International Airport.

"It looks like no one in the world wants to be in the city that week," said Rick Silver, a partner at Mad River Management. The seven-person financial services firm is among the companies planning to stay open convention week by allowing employees to telecommute.

"We're assuming that our people collectively don't want to come to work that week, and they'll do anything to avoid it. I will try to be as far away from the thing as possible," Silver said.

Liberty Mutual is accommodating vacations and staggered hours for its 1,700 downtown employees, spokeswoman Adrianne Kaufmann said. The company also is providing transportation updates on its internal Web site and working with food vendors and courier services to ensure deliveries get through.

UPS and FedEx also are making plans to keep the deliveries flowing. Not only will they have to deal with road closures to get packages delivered, they also have to get to and from the airport.

Not far from the convention site at Massachusetts General, the city's biggest hospital, ambulances will radio ahead to access blocked-off roads.

While some restaurants and hotels expect a big jump in business, others aren't so sure. More than 30,000 media representatives, delegates and convention visitors are expected.

"I expect a trade-off at best," said Dave Devine, owner of Mulligans, a hole-in-the-wall sandwich shop across from FleetCenter. "Close to 90 percent of our customers are regulars from downtown offices, and they're all listening to the mayor and taking the week off."