Twelve years ago, a Harvard maintenance worker was doing routine work in Holyoke Center, when he noticed a small crack in one of the concrete slabs that supports the outside walls of the building.

"It was a minor problem, so we just watched it," recalls Robert J. Burbank, an official with the University's Construction Management Department.

But because of neglect, that one tiny crack has grown into a major headache for Harvard, as many of those so-called "fins" crucial to holding up the building have started to crumble.

Harvard will undertake a $1.2 million reconstruction project the shore up the building, which houses many central administrative offices.

The bulk of the repairs will involve replacing the concrete fins with 1300 aluminum fins. Already, about 250 of these supports have been removed in favor of wooden supports, though officials say most of the work will be done this spring and summer.

While officials know what has to be done, they appear unsure about why exactly repairs are needed for a building that was built at a cost of $12 million and designed by a world-rek`nowned architect.

The 10-story building, constructed in 1965, was designed by Josep Luis Sert, a former dean of Harvard's Graduate School of Design. Sert won several architecture awards for his plans for the structure, which, according to specialists, was very advanced for its time.

"Sert tried new innovations with a new type of surface," explains Hooker Professor of Visual Art Eduard F. Sekler. Sekler notes, however, "Anytime you try innovations, you run a certain risk."

Still, officials are not sure about where to assign blame for the problems suffered at the building.

"It could have been a deficiency in the design or in the construction or both," says Burbank.

The administrator speculates that the apparent frailty of the supporting slabs might have something to do with the material used, a relatively inexpensive form of concrete that may have been unusually susceptible to the vicissitudes of New England's weather.

Still, this doesn't fully explain everything, especially the apparently inexplicable fact that the damage to the fins is isolated to only one half of the Holyoke Center complex--the part nearest to Dunster Street.

The other half, the part which houses the University Health Services and Stillman Infirmary, is of similar design and construction. But, say officials, no problems have emerged nor are any expected.

As an official with Harvard's real estate office, David Zewinski, says of Holyoke's woes: "It's like a five-car accident at an intersection. You just can't tell what caused it."

Although the crumbling fins pose the major threat to the building, there are other problems as well--particularly a faulty heating and air conditioning system.

"It could be 38 degrees out, and some parts of the building will need cooling," says Zewinski, explaining that this is part of a fundamental design flaw in the building "that should have been corrected long ago."

Harvard is now paying the price of the negligence of the cooling system--to the tune of $1 million. And other minor repairs have to be made as well, including fixing up the roof and the draping.

Officials strees that all this construction should not greatly disturb the building's workers and bureaucrats. And these tenants themselves express little concern about the pending renovations.

Says one worker in Harvard's benefits office inside Holyoke. "I'm less concerned now that I know something is being done than when they had just the wood there."