The Environmental Protection Agency expects by Aug. 1 to add 100 to 150 hazardous waste dumping sites to the existing list of priority Superfund sites designated for quick action, William N. Hedeman Jr., director of the Superfund program, said yesterday.

Hedeman said the Superfund office is also mapping out proposals to:

* Determine which chemical contaminants in a dump site are already controlled under laws like the Clean Water Act and the Safe Drinking Water Act and enforce the existing standards "to the extent . . . appropriate."

* Establish procedures for determining how thoroughly each site should be cleaned. The process would require an estimate of the health risks posed by pollutants for which there are no standards, a projection of the costs of reducing those risks and a balancing of the two estimates to meet the cost-effective requirements of the 1980 Superfund law.

* Set a time limit--most likely two months--for EPA negotiations with industry to determine how clean-up costs will be divided between industry and government. If no agreement is reached within that time, the agency could go to court to recover what it determines to be industry's share of the cost.

The proposals, likely to be studied for months before they are unveiled, were greeted with cautious praise as "a step in the right direction" by Khristine Hall, an attorney for the Environmental Defense Fund, which sued the EPA last year in a challenge to the original Superfund regulations.

The Superfund office, which until January was under the authority of former assistant administrator Rita M. Lavelle, was the birthplace of the scandal that led to the resignation of a score of EPA officials, including Lavelle and former administrator Anne M. Burford.

Hedeman said yesterday that six of the 419 "priority" dumps have been cleaned, 22 more are being cleaned, 90 to 100 are being studied and the remainder are the focus of state action or negotiations between the EPA and industry to determine who should pay for the clean-up.

Other officials estimate that 1,500 additional sites may pose serious hazards, but current funding would not permit investigation of the sites before the Superfund law expires in 1985.

The clean-up of a hazardous site costs an average of $6.5 million, Hedeman said. When enforcement and overhead costs are subtracted from Superfund's $1.6 billion treasury, he continued, enough money would remain to clean up only 170 sites.

Hedeman said that the proposals are an attempt to solve a problem that has bedeviled negotiations since the fund was established to expedite clean-up of some of the 14,000 closed or abandoned sites where hazardous chemicals were dumped. Effective enforcement of the law requires EPA to answer the question, "How clean is clean?"

"When you're dealing with a hazardous waste site, you're dealing with the indiscriminate dumping of a variety of chemicals which can be harmful themselves but can also have a synergistic effect in combination," Hedeman said. The EPA must determine what chemicals are present and how dangerous the pollutants are, individually and in combination.

Hedeman said that then the EPA can decide how to clean up the site.

The EPA does not plan to establish new standards for unregulated chemicals, and Hedeman said that the agency is shying away from a nationwide standard of acceptable risk that would apply to all dump sites. He said the EPA wants to select clean-up methods on a case-by-case basis.