Long-time private supporters of the Fogg Art Museum yesterday assailed President Bok's decision to end a three-year expansion plan, warning that the move would severely restrict the University's ability to raise money and threaten Harvard's traditional preeminence in the field of Fine Arts.

Major donors to the Fogg's on-going fund drive and members of the Fine Arts faculty said that Bok's decision was based on unsound economic reasoning, overly cautious planning, and an underestimation of the Fogg's significance within the University and in the museum world.

Donors serving on the supervisory Visiting Committee for the Fogg confirmed a recent public statement by Fogg Director Seymour Slive that millions of dollars pledged to the museum addition have already been lost because supporters have withdrawn donations in the wake of Bok's decision. In the future, these sources added. Harvard's main capital fund drive may lose substantial support from benefactors angered by the sudden cancellation of the Fogg expansion.

"I'm through with Harvard, I would not give them another red cent," said Ruth Carter Johnson, a Visiting Committee member and chairman of the board of the Amon Carter Museum in Ft. Worth, Texas.

Ralph F. Colin, a leading Fogg fund-raiser and high-ranking official with the Museum of Modern Art in New York City, leveled the most severe charge at Bok, saying in a private letter mailed to the president Thursday that his decision would cost the Harvard Campaign "far more" than the $3 or $4 million which became the issue of debate just before Bok killed the expansion plans.

Painting a picture of repeated administrative mismanagement resulting from an insensitivity to the needs of the Fogg, Colin said in his letter, "There seem to be only two alternatives. Either a.) You are unaware of the Fogg's role and importance as are the other five members of the Corporation, or b.) Being aware you are unwilling to go to bat and if necessary lay your job as president on the line to accomplish what needed to be accomplished. You may therefore take your choice as to whether 'ignorance' or 'ignominy' more aptly describes the basis of your behavior."

Although Colin was the most outspoken of Bok's critics yesterday, others who received copies of Colin's letter echoed his sentiments and predicted hard times for Harvard arts fundraising in the future.

Bok refused comment on Colin's letter, but he reiterated the reasons for his decision as he originally stated them in a private letter to members of the Visiting Committee dated February 2. Bok said that fears over unanticipated construction and operating costs, the difficulty of perhaps maintaining unconnected buildings, and reservations about a recent and highly controversial proposal to sell Fogg paintings to raise more money were major reasons for his decision.

"In the end, of course, one can always ask why the University would not simply dig into its own resources and contribute the remaining $3 or $4 million required," to complete the building. Bok stated "I can only say that present conditions are extraordinarily unfavorable for making additional contributions of this magnitude."

During interviews with members of the Corporation and other University officials, it also became apparent this weekend that a lack of faith in architect James Stirling's ability to complete the project within the original budget also contributed to Bok's final decision.

Stirling's "general attitude was the most serious source of worry," George Putnam '49, treasurer of the Corporation, said. It was the first time that University officials publicly disclosed fears about Stirling's ability to manage the project successfully.

The winner of numerous international architectural awards, the British designer was chosen for the Fogg expansion project in 1978 after a yearlong search.

Corporation members also defended Bok's decision to abandon Stirling's design by saying for the first time that they expect within the next few years to complete an alternate museum expansion plan.

"The Corporation expects an addition of the Fogg to be built," Putnam said. But he added that it "will be a more practical one. The consensus way, this wasn't the right one."

Fogg officials and several donors have said that they were unaware of any alternate expansion schemes.