Proposed regulations to set new chemical standards for the drinking water of large cities were attacked yesterday by critics as too costly and perhaps unnecessary, but defended by supporters as needed to reduce the risk of cancer.

Opponent William Hudnut, who wryly noted that as a congressman he cosponsored the 1974 Safe Drinking Water Act that authorized the Environmental Protection Agency to issue such regulations, told an EPA public hearing the proposals "carry a logical concern to a mistaken extreme."

Hudnut, now mayor of Indianapolis, opposed the proposed regulations as inflationary and as "untried techniques to deal with uncertain problems."

Consumer advocate Ralph Nader, however, charged opponents of the proposed regulations with waging "a campaign of obfuscation, deception and intransigence."

Water works professionals "favor continued exposure of the public to cancer-causing chemicals" by objecting to the proposals, Nader said. He referred to one group, the Coalition for Safe Drinking Water, as the "Coalition for Unsafe Drinking Water."

The EPA regulations, proposed in January, would limit the level of certain cancer-causing organic chemicals in the water supplies of cities with populations exceeding 75,000. Smaller cities would not be affected.

About 65 cities that draw water from sources especially susceptible to cancer-causing pollutants would be required to install special filtration systems.

EPA estimates that the regulations would increase water costs between $616 million and $831 million for the cities involved. The annual water bill for a family of three would rise between $7 and $23.

Opponents of the regulations dispute EPA's estimates. Charles Buescher Jr. of the Coalition for Safe Drinking Water estimates the capital costs at about $4.5 billion, about six times the EPA figure.

Donald Kennedy, commissioner of the Food and Drug Administration, and susan King, newly appointed head of the Consumer Product Safety Commission, appeared at yesterday's hearing to support the EPA proposals.

Kennedy called them "another major step toward full implementation of the Safe Drinking Water Act," and said he "applauded" EPA's action.

King defended EPA's methodology in defining cancer risks. That methodology had come under sharp attack from critics of the proposals.

George Pendygraft, speaking for the Coalition for Safe Drinking Water, said the proposals "appear to us to be based upon fear, not upon fact." He disputed EPA's view that certain chemicals posed a sure risk of cancer and clled for more "hard work and research" to define the risks.

While most water works professionals at the public hearing opposed the proposed regulations, Robert McGarry, general manager of the Washington Suburban Sanitary Commission, applauded EPA.

The WSSC "strongly endorses the proposed regulations" and has already taken steps to comply even though the EPA has not issued its final statement, he said.

"We agree with EPA that synthetic organic chemicals and trihalomethanes are a health risk and, furthermore, we agree that the regulations as proposed are a practical solution for this problem," he told the EPA panel.

He said surveys and correspondence with consumers show that WSSC water users are concerned about the quality of their drinking water and are willing to pay to reduce health risk.

Later, he labeled opposition to the proposals by other water works professionals "a knee-jerk response."

"They feel we've always done it that way, and so it is good enough."