The tiny National Consumer Cooperative Bank, having just defeated the White House in a David-and-Goliath battle for survival, has found itself recast as an uncooperative giant in an attempted coup by a band of Lilliputian co-ops.

To thwart the attempted co-op coup, the bank's board recently scrapped a longstanding co-op tradition. The board changed the one-cooperative, one-vote rule by which board members are elected and instead adopted a system that gives more votes to bank borrowers and large co-ops.

The rule was changed after an unexpectedly large number of small co-ops from across the country bought stock in the bank in the past month so they would be eligible to participate in the election of new board members for the bank. The change was made seven weeks after election procedures started and was criticized for its timing even by some who support a new voting formula.

NCCB President Carol Greenwald acknowledged that there were "political realities" involved in the decision to change the one-cooperative, one-vote rule.

"If one group has predominant weight, you breed the suspicion of the bank by the other groups. . . . We wanted to take the bank out of the politics of the co-op movement," she said.

"We know it was an organized effort," Greenwald said, adding that it was "very short-sighted" on the part of the smaller co-ops to try to take control. "They were going to set up a dynamic where they would alienate larger co-ops." he board's action immediately drew fire from a nonprofit co-op bank monitoring group that other informed sources said had organized the campaign to take over management of the NCCB to refocus the bank's efforts to smaller, low-income and counterculture cooperatives. These included "new wave" co-ops, such as those for natural foods and bike shops and others intended to promote alternative lifestyles.

"When Co-op Bank management realized that its relationship with the co-op movement was deteriorating and that management-backed candidates would not be elected, they engineered a change in the voting structure to avert their loss of control," charged the Co-op Development & Assistance Project in an editorial written for an upcoming newsletter. "Betrayed this time, co-ops have no reason to believe the NCCB won't violate due process again."

The bank earlier this year survived attacks from another quarter, having waged a successful battle against the Reagan administration, which wanted to kill it. The quasi-governmental organization was allowed to continue in the federal fold through the end of the year, when it must start relying on the private markets for future financing.

The bank was created to provide loans for consumer cooperatives, which traditionally have had trouble in getting financing from conventional banks. he election of nine new members to the 15-seat board was announced on Sept. 9. Both bank borrowers and nonborrowing stockholders in the bank are eligible to vote, and the bank gave co-ops until Oct. 9 to buy stock so they could participate in the election. Ballots are to go out in December and must be returned by Jan. 15.

By Oct. 9 the number of co-ops eligible to vote had doubled because of a flood of stock-buying by nonborrowing groups, almost all them small ones, Greenwald said.

She pointed out that one-third of all board members are elected every year, and the bank's board wanted to avoid a situation in which different factions would jockey for dominance at each election.