Tufts students returned to classes Monday after five extra weeks of winter vacation, following an unexpected administrative decision last December to mothball most university buildings because of the fuel shortage.

Administrative officials at the university say they have no regrets about the closing of 12 campus buildings from December 18 to March 8.

"If we knew then how warm the winter would be, I doubt we would have closed, but how can you know that unless you're God?," James M. Steindler, dean of students, said yesterday.

The 14-week spring semester will continue into the second week of June to make up for the weeks missed, with no spring recess and a shortened final exam period.

"It was nice having a long vacation, but it's ridiculous trying to find work in the middle of the winter, so I had to live off my parents and friends," Peter Arteaga, a junior at Tufts, said yesterday. "I don't know anyone who did anything, and now it's going to be a really rough semester."

Following Tufts's winter study session in January, most campus buildings remained closed through March 8, forcing the 2700 undergraduates to find temporary jobs, go home, travel or sit it out. The 250 students who remained on campus moved into one dorm, after obtaining permission from the occupants of each room.

The university incurred a cost of about $10,000 as a result of the reshuffling of students, faculty and administrators into fewer buildings, John Mitchell, vice president for business affairs, said yesterday.

Tufts was the only college in the Boston area to undergo such substantial rescheduling, being heavily dependent on Texaco white fuel which was cut by 25 to 30 per cent during the winter months. The Tufts Medical School, which receives steam heat from Boston Edison, remained open.

"The administration threw the decision to close at us [students] last December, and although they took a token faculty vote, students had no say in the matter," Artega said. "People aren't talking about it anymore. Everyone is just plunging into their work."

"I hope none of the students sat on their fat duffs during the break," Steindler said. "It was more difficult for everybody, but I'm personally convinced that given the facts, or lack of facts last December, we did the only responsible thing."