While ''Sewergate'' - the battle over EPA's hazardous-waste cleanup activities - rages unabated, another pollution-related problem is waiting quietly in the wings.
Almost all major environmental laws have now expired. Some, such as the Clean Air Act, ran out more than a year ago.
That doesn't mean the US Environmental Protection Agency's pollution control grinds to a halt. Such activities can continue on the authority of budget bills passed every year. It does mean Congress has missed its own deadlines for overhauling US environmental laws - laws which one environmentalist admits are often ''experimental'' when they're passed. And it creates hundreds of legal snafus. Many counties, unable to meet Clean Air Act deadlines they say are unrealistically stiff, face tough sanctions.
Environmental laws, like much of the legislation Congress passes, are often not designed to last forever. They include deadlines or expiration dates when Congress is theoretically supposed to modernize the law - touching up parts that have proved unworkable or adding provisions to deal with problems unforeseen when the original bill was passed.
The list of expirations reads like a Who's Who of environmental law. The Clean Air Act and the Pesticide Act expired on Sept. 30, 1981. A year later, the Safe Drinking Water Act, the Resource Conservation and Recovery Act (which governs much hazardous-waste disposal), ocean dumping authority, and most of the Clean Water Act ran out.
''What's expired? Just about everything except Superfund,'' sighs Virginia Gibbons, director of EPA's legislative division. The Superfund consists of $1.6 billion allocated by Congress to help pay for cleanup of the most hazardous dump sites. Congress has tried to do its duty and pass reauthorizations on time. But in almost every case, environmentalists and industry have taken entrenched positions on either side of a controversial provision, shaking their fists and helping to stop the reauthorization effort. The Clean Air Act, for instance, has been stalled, in part by fighting over the touchy subject of acid-rain controls.
The White House's less-than-deft handling of environmental issues has contributed to the jam-up. An early administration draft of a new Clean Water Act horrified environmentalists with its sweeping changes. And now the issue of Reagan administration policies on hazardous waste clean-up is threatening to swamp all attempts at reauthorizing environmental bills.
Six congressional committees are now investigating EPA's administration of Superfund. Will this halt movement on environmental bills?
''That's a very important question. It is certainly sidetracking us,'' says a top Senate environmental committee staff member.
But that doesn't mean pollutants will start pouring back into the air and water. The effects of allowing pollution laws to expire are more varied and subtle than that.
First, US environmental law will not reflect the best scientific knowledge.
''Scientifically, this is a new area where you're getting new information all the time,'' says Steven Pearlman, political director of the League of Conservation Voters, ''and reauthorization opens the door for considering changes we now know we need.''
Acid-rain controls, say environmentalists, are one example of this. Other controls - such as certain provisions of the Clean Air Act - may have proven unrealistic, and need to be relaxed.
Second, expiration can create a mass of legal problems. The most glaring example of this is the Clean Air Act.
Many US counties have been unable to meet air-quality deadlines set by the act, and EPA says it must slap the offenders with penalties, such as restriction of federal highway funds or air program grants.
''Some of these sanctions are environmentally counterproductive,'' complains William Becker, Washington representative for state air-pollution program administrators.
Sen. Robert Stafford (R) of Vermont, chairman of the Committee on Environment and Public Works, is expected to reintroduce Clean Air legislation this week. But progress is uncertain, as Senator Stafford's staff is tied up with such Sewergate-related tasks as obtaining the desk calender of former EPA assistant administrator Rita Lavelle.