A nationally known, multimillionaire Harvard graduate is providing much of the anonymous financial backing for Samuel P. Coffman's $7.6 million bid and $100 million development plans for the Bennett St. MTA Yards.

The mysterious financier, who has been identified as a member of an extremely wealthy and well-known Harvard family from outside the Boston area, is remaining anonymous because he does not want to be discovered as bidding against Harvard. Five additional, but apparently lesser backers may also be behind Coffman.

According to Coffman, "the man is an alumnus intimately related to the University, a man above Marshall Field in financial stature." Coffman claimed "there is no man in Boston who could raise the kind of money I am talking about; development plans will run into $100 million."

Board Will Not Demand Information

"If I could disclose the backer there would be no question of my getting the bid," Coffman added. So far Coffman has refused to disclose his financial support to the MTA Board of Directors who must decide on a buyer. However, according to MTA officials, the Board will not necessarily demand such information before reaching their decision.

Coffman's bid of $2 million plus at least $5.6 million in relocation costs for the MTA is more than $2 million higher than Harvard's $5,010,000 bid. However, the MTA Board is not bound to accept the highest bid. Many sources feel that Coffman's high bid will not be accepted since the MTA cannot be sure that his development plans are fully responsible.

Reportedly, Coffman has been negotiating with a large discount house. Other Coffman plans include a Howard Johnson restaurant and motel, apartment and office buildings and a mammoth underground garage. Such plans would involve a zoning change from the Cam- bridge Zoning Board.

In other developments, the MTA put an additional 61,000 square feet of Bennett St. land up for sale. The additional land forms a strip down the center of the Yards. MTA officials expect both Coffman and Harvard to raise their bids for the new land. The new land offer could be seen as an effort by the MTA to force Harvard to raise its bid