The U. S. Product Safety Commission, after an emotional debate that lasted nearly two hours, voted 3 to 2 yesterday to terminate proceedings to require safety hinges on toy chests that have been linked to the deaths of 21 children and two cases of irreversible brain damage in the past 10 years.

The commission voted six months ago to draft a standard that would require toy chest manufacturers to equip them with safety hinges that would hold a lid open at any point in the opening arc. That vote, on Feb. 9, came after the commission members criticized the industry for failing to correct the hinge problem.

But after hearing a report from its staff indicating that 98 percent of the 186,000 toy chests produced in the United States this year will have safety hinges, the commission voted yesterday to terminate the rulemaking proceedings rather than finalize them.

"We don't need to mandate into law something that already exists in reality," Commissioner Stuart M. Statler said. Chairman Nancy Harvey Steorts and Commissioner Terrence M. Scanlon agreed.

" . . . more than 90 percent of the manufacturers have agreed to apply the corrective hinge to these chests and are doing so voluntarily today," Scanlon said. As a result, he said, the commission "ought to defer here to their voluntary efforts, to monitor their activities, and encourage additional and better efforts in this area of toy chests and other children's products."

But blistering dissents were issued by the other two commissioners, Sam Zagoria and Edith Barksdale Sloan.

Zagoria charged that the CPSC, in dropping the rule-making proceedings to require the lid supports, was deferring "to a voluntary standard that doesn't exist," since the proposed industry guideline hasn't yet been written into a code.

Sloan wasn't present for the meeting, but she had left instructions to cast her vote to finalize the mandatory rule. She also had prepared a three-page statement on the issue, expressing skepticism that toy chest manufacturers will comply voluntarily.

The staff report on compliance was based on information supplied by the toy chest industry. In addition, the industry told the staff that the required hinge could cost the manufacturer as little as 10 cents. The maximum cost to the manufacturer would be $1.77, the industry said.

Most of the toy chests range in price from about $18 to $85.

Questions about the toy chest lid safety date back to 1973 when the first of the deaths and injuries were reported. The problem with the toy chests occurs when the lid falls against a child's head while he is leaning into the chest or when the lid "merely moves down against the child's head," leaving the child in a position where he can strangle from his own weight, the commission staff report said.

Statler argued yesterday that the agency could move quickly if there are indications of toy chests being sold without the proper lid supports.