Tomorrow is a big day for the thousands of Harvard graduates finally finishing a significant part of their academic careers.

But it's also a big day for the 90,000 or so residents of Cambridge, who are forced to deal with an influx of about 55,000 extra visitors.

"It's crazy around here," said Kathleen M. Schilling, reservation manager at The Inn at Harvard. But the added crowds don't seem to bother the Square's businesses a bit.

Schilling said the Inn's 113 room's are sold out even though this week's prices are almost 50 percent higher than normal. For the added cost, however, guests receive special meals and "110 percent service," Schilling said.

Cambridge tries to be a "friendly host," said Ralph E. Dunphy, deputy commissioner of the department of public works. "The city is glad to help out."

The city puts extra trash baskets in Harvard Square to accommodate the increased crowds, and sweeps the streets before the ceremony, Dunphy said.

"It obviously helps us if people come to Cambridge and say, Wasn't Harvard Square clean and friendly?" Dunphy said.

The city also gives consideration to the parking concerns of the week's visitors, city Parking Coordinator Philip A. Leccese said, allowing alumni with reunion logos to park in permit areas.

Alumni and families of graduates made reservations at Upstairs at the Pudding up to a year and a half in advance, said restaurant co-owner Mary-Catherine Deibel.

Deibel said this year will be the restaurant's largest graduation, partly due to the herb garden patio they recently opened to diners. The restaurant will serve special dinners and host alumni groups throughout the week.

Some preparations, however, are a bit more low key.

"We don't really go in for the hoopla, souvenirs and all," said Paul J. Macdonald, manager of the tobacconists Leavitt & Pierce.

Macdonald said his 110-year-old shop is "like a beacon in the night," for alumni in a Square much-changed since previous visits.

The store provides a "relaxed atmosphere" in which visitors can browse, and gives free cigars to alumni and graduates on Commencement, Macdonald said.

Of course, stores dealing in Harvard paraphernalia appreciate the visitors.

J. August Co. assistant manager Maurice, who would not give his last name, said that their store offers a 10 percent discount on all merchandise to "kick off" the summer.

He said the store gets a lot of business from seniors, who seem suddenly to realize, at the end of their four years in Cambridge, that this is their last chance to get "something of Harvard."

Harvard insignia sweatshirts have been the store's most popular item, as they are at the Coop, along with shirts and hats.

Coop President Jeremiah P. Murphy '73 said Commencement week doesn't beat early September, book-buying period, in sales volume, but it is peak season for the insignia items.

"People seem to be in a better mood this year [than last year]. That means a lot," Murphy said. He expects tomorrow to be the biggest sales day.