Harvard Square became a boomtown over the summer: as several new buildings sprang up in what were vacant lots when students left in May.

In the northeast corner, the addition to the Fogg Art Musueum took shape, while in the southwest the Kennedy School of Government extension, the University Place office and condominium complex, and the new Coolidge Bank appeared, all contributing to the largest volume of simultaneous development in the area since the beginning of the century.

The University itself also got a new look as four Houses were overhauled, the year-long renovation of Sever Hall-one of Harvard's most widely used classroom buildings-was completed, and a tiny little guardhouse popped up outside Mass Hall.

The most striking change is in store for old-timers returning to the Square by subway. Instead of emerging in front of the Coop, they will surface a block away, in front of Store 24.

As the latest phase in the Red Line extension (1). the Massachusetts Bay Transportation Authority shut down the Harvard/Holyoke stations along Mass, Ave, and the Harvard/Brattle station near the K School. In their place, they opened up new terminals on Church St. and outside Johnston Gate. The shift was only the most visible sign of progress in the sprawling project, which has gutted the Square for five years and is expected to continue for another 18 months. The Square work is part of a $72 million project, which by 1986 will stretch subway service north beyond Harvard through Porter and Davis Squares, ending at Alewife.

Gov. Michael S. Dukakis kicked off the station switch, personally inspecting the new sites on Wednesday, August 31. At 10 p.m. the next evening, the Harvard/Holyoke tracks carried their last car, and the construction crew worked feverishly over the Labor Day weekend, drilling and hammering past midnight, and pulling in double and triple overtime pay. (Authority officials picked the weekend to make the transition, when commuter use would be relatively light. In the interim, the MBTA provided free bus rides to and from Kendall Square).

The first train at the new station picked up passengers at 5:24 a.m. September 6 and few hitches marred the milestone even-though supervisors did inaccurately estimate the height of all cars, and as one tall train pulled into the station it smashed a security camera.

The inaugural run came close to being indefinitely delayed. A week before the scheduled change-over, the state revoked a 1978 waver which would have allowed the new station to open before making it accessible to the handicapped. After two hectic days of negotiations, the MBTA worked out a compromise: the Authority now offers a shuttle bus service. Officials estimate about two people a day will use it.

Other new features of the project include as underground waiting station for all buses leaving Harvard Square, and the capacity to hold six-car trains, two-more than the old set up.

When the mess is finally cleaned up, the Square will have a new look, with trees and wider sidewalks. Eventually, a new entrance near the defunct Harvard/Holyoke stop will open up, completing the eight-year project.

On the corner of Broadway and Quincy Streets, the Fogg Art Museum (2) is working to alleviate its creamped research and display facilities by raising the Arthur Sackler extension. Much of the exterior has already been completed, and the whole project complicated by special temperature and humidity control considerations is expected to be done by the spring.

Officials are still not certain about the fate of one feature of the building. The museum hopes to have a bridge over Broadway connecting its two buildings to avoid deterioration and security risks of transportating artworks back and forth. But it must first go through a byzantine community approval process which, according to associate Acting Director Robert Rotner, will probably not conclude before construction ends.

The other major Harvard project will expand one of the University's fastest growing divisions, the Kennedy School of Government (3). The skeleton of the Belfer Center for Public Management is complete, and construction planners expect the addition's exterior to be finished by Thanksgiving.

Down Mt. Aubum St. across from the post office, more than 200,000 square feet of office and retail space in University Place (4) should open by December 1. At that point, construction at the Harvard-owned project will shift toward an adjacent complex University Green where 75 high-priced condominiums will go on sale.

Behind University Place and further west, workers are just finishing the foundation for another condo/office complex. The Charles Square (5) Development, on Bennet St. and Memorial Drive, will have a 700-car parking garage, 86 luxury condominiums, 40,000 square feet of retail space, a 110,000 square feet office complex, as well as a 300-room luxury hotel and a water front park on the drive.

Rounding out the activity in the southwest part of the Square is the Coolidge Bank (6) development on Brattle Square. The original building was demolished last winter, and bank officials have been operating in a trailer surrounded by the new structure's girders. The new bank was originally slated for completion by November, but now will not be finished until March. When it is built, the bank will also rent out office space.

Development fever spread even to stable, historic Harvard Yard. Sever Hall (7), which was built in 1880, was retooled at the price of $6.3 million. The aging facility, which was criticized for poor acoustics, noisy hunting, and deteriorating furnishings now sports air conditioning, an elevator, access for disabled students complete audio-visual capability and a library for the Extension school.

By cleaning out areas previously used for storage classroom space expanded from 25 to 30 rooms. One quibble that has arisen about the new look is the colon Shades of purple have replaced the old green and beige While some officials praise the change, President Bok, upon touring the facilities, reportedly sighed and said. Well at least they didn't do it in polka dots.

Harvard's newest and smallest building was completed in early July. The live loot by live-foot-by-five-foor gatchouse inside Johnson Gate (8) was the end product of three years of haggling 800 designs by one of the Boston area's most prominent architects, and $25,000 from University coffers.

The construction followed President Bok's proposal to reduce automobile traffic in the Yard by closing the gate behind Widener Library and making the Johnston area the main entrance. That request required a gatehouse for guards direction traffic but raised complaints from the Cambridge Historical Commission which discouraged any tampering with the three century old handicapped Designet Graham Gund appeased all sides with a colonial era plan. The facility is more modern inside equipped with a telephone lamp seat space heater.