In the face of intense protests from environmental groups and a handful of firms, the Environmental Protection Agency yesterday reimposed a ban on disposing hazardous liquids in landfills, but with some revisions that would allow a small amount of liquid to be disposed.

Under the new orders, after Friday, landfills will not be allowed to accept barrels containing "free-standing" hazardous liquid. The liquid must be siphoned off, or absorbent material placed in the barrel, or the contents solidified. EPA estimates that this would allow only 5 percent of the barrel's contents to be liquid.

EPA banned the disposal of any liquids in landfills from Nov. 19, 1981, to Feb. 25, when it lifted the ban for 90 days while it developed new standards to allow up to 25 percent of a landfill to hold containers filled with hazardous liquids. EPA still plans to go ahead with those standards, which environmental groups oppose. Companies had been storing liquid wastes since November, when EPA informed them that the ban would be modified.

EPA's move to lift the ban outraged environmental groups and some congressmen and state and local officials. Two firms that had developed alternate disposal methods and the Environmental Defense Fund went to court to try to stop the agency.

EDF attorney Khristine Hall said EPA's latest action "sounds like a reasonable approach. It retains the essential concept of the ban while giving the flexibility needed to take into account some practical problems. But EPA could have done this a month ago" instead of allowing industry to dump its liquid waste for a month.

"Essentially EPA is admitting it made a mistake. I'm hoping this is a turning point in the agency's activities in this area," said Hall.

Rep. Guy Molinari (R-N.Y.), who has criticized the agency's handling of the issue, called yesterday's action "an admission of error." He said what is "bothersome is the manner in which they handled this entire affair." Molinari said EPA should have gone through the rulemaking process, which would have given critics time to act, rather than lift the ban with no public warning. "The question really is: how much has been dumped prior to this reversal of ruling?"

Hugh Kaufman, assistant to the director of EPA's hazardous-site control division and a critic of his agency's handling of the issue, said the latest decision "allows liquids in landfills as long as it's mixed with kitty litter. It will still leak out. It may just take an extra six months." He also noted that the liquid would not have to be treated to remove dangerous contaminants.

Gary N. Dietrich, director of EPA's Office of Solid Waste, agreed there "is probably no way to build a leakproof landfill." Dietrich said the extent of the threat depends on whether the landfill has a liner or collection system, the distance between the landfill and groundwater supplies, and the type of soil. Clay soil, for instance, will absorb more of the toxic material out of the water than sandy soil.

The National Solid Wastes Management Association, the trade group of the disposal industry, called EPA's decision "a political masterstroke and a workable environmental regulation." Spokesman Richard L. Hanneman said the association's major concern was that the November ban prohibited "one drop of liquid" in containers, something the members did not feel was reasonable.

Hanneman added that the association would like EPA to allow waste producers to certify that there is no liquid in the barrels before shipping them, so that operators of disposal facilities would not have to open every barrel. Dietrich said certification will now be allowed, although the ultimate responsibility will rest with landfill operators.