Weekend forecast: slow going

Mix two Red Sox home games with five college commencements. Add in free tours on a storied aircraft carrier on the brink of the scrap heap. Then spice up the mixture with visits from the prime minister of Greece and from a prime security focus, the president of war-torn Afghanistan.

The recipe this weekend may be a delectable prospect for Boston businesses, but all the visitors could add up to chaos on the city's streets and public transportation network. Wherever the foreign dignitaries travel, they could be preceded by massive security and rolling road closures.

''Our concerns are that any time you have this many events in a short period of time, with it comes some headaches," said Thomas J. Tinlin, acting commissioner of the Boston Transportation Department. ''We're working with federal, state, and local law enforcement to make sure people can move around the city as best as possible during the weekend."

The Massachusetts Bay Transportation Authority is adding subway and commuter rail service across the region and shuttle buses from downtown to the USS John F. Kennedy, anchored at Marine Industrial Park in South Boston. Boston police have declared the weekend an all-hands-on-deck situation. Secret Service and State Police won't say where, when, or even whether troopers will close down city arteries while dignitaries are whisked to events.

What is clear, though, is that the exits to Storrow Drive from Interstate 93 will be closed all weekend because of road demolition work.

''People should give themselves plenty of time to get where they need to go," Police Superintendent Robert Dunford warned yesterday. ''And they should use public transportation if possible."

For anyone caught up in traffic snarls, city-sponsored roadside music performances may quiet the nerves. Then again, they could add to the congestion. The performances are part of the celebration of Boston's 375th birthday, which kicks off this weekend and features a 2-mile walk around the Back Bay perimeter tomorrow and offers live music along the route.

Forecasters say it may be a soggy weekend, but few events have been canceled.

''This is going to be an incredible, incredible weekend," gushed Larry Meehan, director of public relations and tourism for the Greater Boston Convention and Visitors Bureau. ''I don't think it's going to matter if it rains."

Hotels across the city are booked nearly solid tonight. On one website yesterday, the average price of rooms still available was $352. A basic double room at the Days Inn along Route 1 in Saugus was going for $252. Industry representatives call it compression.

''When the city gets full, it automatically pushes people out to the 'burbs, which is a great thing," said Art Canter, president of the Massachusetts Lodging Association.

The busy weekend gets underway today with seven graduations in Greater Boston and the arrival of Afghanistan's president, Hamid Karzai, at Logan International Airport this afternoon.

Karzai is scheduled to speak at Boston University's commencement tomorrow, but he will not throw out the first pitch or even attend the Red Sox game tonight at Fenway Park, according to a State Department official who spoke on the condition of anonymity. Security officials scrapped the plan Thursday because of the difficulties of crowd control at the ballpark, the official said.

The prime minister of Greece, Kostas Karamanlis, arrived in Boston last night and is scheduled to give the commencement speech tomorrow at Tufts University.

While authorities downplayed yesterday the impact of the high-profile dignitaries on traffic, simultaneous stops in Boston by the president of Pakistan and Vice President Dick Cheney in June 2003 ensnared thousands of motorists in traffic jams. The rolling closures, which lasted about 20 minutes each, created virtual parking lots on sections of Route 128.

''There may be some inconveniences, but I don't think they will be large, and it's definitely necessary," said Steven Ricciardi, special agent in charge of the Boston field office of the US Secret Service.

Besides the foreign dignitaries, thousands of sailors and Marines are in town for the weekend for Armed Forces Day. Today, hundreds of Marines will parade in South Boston, forcing buses to detour.

Much of the increased subway and commuter rail service is for crowds visiting the USS John F. Kennedy aircraft carrier, docked in South Boston.

The T's Blue, Orange, Red, and Green lines will run more trains and trolleys, and Transit Police staffing has been beefed up.

''I have absolute confidence in our service and security plans for this extraordinary weekend in Boston," MBTA General Manager Daniel Grabauskas said yesterday.

Jeff Larson, general manager of the traffic reporting firm SmartRoutes, said there was no cause for alarm.

''This city has had graduations for a long time, and they've happened on the same day of Red Sox games before," he said. ''Around the schools there may be some congestion but nothing major. There will be localized traffic problems, and if you're stuck, it will be frustrating, but I don't foresee this entire city being gridlocked for the weekend."

In any case, the recipe could be repeated in the coming months, albeit with different ingredients.

''Every weekend, starting in May and going through the fall, there are parades, festivals . . . . . There's an awful lot going on in the city that people can take advantage of," said Dunford. ''This is just the kickoff."

Farah Stockman of the Globe staff contributed to this report from Washington. Donovan Slack can be reached at dslack@globe.com.