Consumer activist Ralph Nader predicted a major expansion of consumer cooperatives as a result of Senate legislation passed Thursday that would provide loans to start such cooperatives.

Esther Peterson, President Carter's consumer adviser, and Nader both said the bill, by creating more cooperatives, would help develop economically depressed inner-city and rural areas.

The bill, a scaled-down version of one passed by the House last summer, would authorize $300 million over five years to create a National Consumer Cooperative Bank, which would provide market-rate loans and technical assistance to cooperatives.

The Senate bill, passed 60 to 33 after a day-long debate, will now go to a conference committee to resolve differences with the House bill, which would establish a $500 million bank.

Passage of the Senate bill came after the Carter administration reversed its position against the House bill, deciding in January to support a limited version of the House bill. Roger Altman, assistant secretary of the Treasury for domestic finance, explained then that the policy change resulted from "a better appreciation (by the administration) of the needs of consumer cooperatives."

Approval of the bill became certain Thursday after the rejection of an amendment to change the proposal into a $20 million two-year study and pilot loan program designed to test the program's feasibility.

The bill was opposed by small-business groups, who argued that the cooperative bank would put them at a disadvantage in obtaining capital for expansion.

Peterson said the bill would not harm small businesses. "The Small Business Administration is dealing very, very well with small businesses. They have plenty of opportunities to obtain financing," he said.

Nader said the bill would provide to cooperatives a source of funds similiar to what the SBA provides to small businesses. He said small businesses have abandoned many inner-city and rural areas that cooperatives could rebuild.

Nader said cooperatives give consumers "the muscle to fight inflation and monopoly." Co-ops can lower prices considerably and act as a counterbalance to store chains, he said.

The measure would empower the Cooperative Bank to make loans totaling five times its paid-in capital plus other earnings. The bank would eventually be owned by cooperatives that purchase its stock from the government. The bill also would provide $75 million in technical assistance and low-interest loans to stuggling cooperatives.

Senate opponents of the bill argued that it was not in keeping with the administration's promise to reduce the number of government agencies and to limit government intervention in the private sector.

An estimated 50 million Americans belong to cooperatives, in which the customers of a company are also its owners, providing such goods and services as groceries, car repairs and health care.