The building industry is expected to follow with interest the results of two developments in sewerless sanitation at the end of the year.

On the last day of its 1977 session Congress passed amendments to the Federal Water Pollution Control Act of 1972 (now re-named the Clean Water Act). President Carter signed the bill on Devember 27.

Several environmental organizations were unhappy about provisions of the bill that extended the dates for installing more effective pollution-control equipment. But environmentalists and real estate developers can both be pleased with some little noticed provisions that recognize the value of on-site (sewerless) toilet systems.

Under the new legislation, EPA is directed to set up a national information clearinghouse for research into innovative sanitation technology. This technology includes such alternatives to traditional methods as land spraying of sewage and on-site toilet systems.

In addition, EPA now has clear-cut legal authority to grant 75 percent of the cost of on-site systems (as it has long done for municipal sewer lines and treatment plants) for dwellings that were built before the new act. Such grants cannot be made to an individual person but must be made to a public body such as a local sanitary district, which inspects and maintains each household treatment system.

For example, a sanitary district could install the new aerobic tanks for dwellings in a rural area or a small town where septic tanks had failed, with assurance that qualified personnel would be on call to remedy any mechanical problems. EPA must determine that the on-site systems cost less than a centralized collection and treatment system. The agency is to set aside 4 percent of the money allotted to rural states for alternative systems in communities of 3,500 or less.

Sen. Jennings Randolph (D-W. Va.) chairman of the Senate Environment and Public Works Committee, pointed out that one town in his state, Hepzibah, W. Va., would need about $8,000 a house to install a central sewerage system and treatment plant.

These new provisions recognize what real estate developers and sanitary engineers are learning every month - that sewer lines hooked into a central sewage treatment plant may be fine for a concentrated municipality but are unduly costly for a community of scattered houses in a semi-rural area.

Estimates to install a sewer system and treatment plant in a rural section of Fairfax County were recently reported to run more than $9,000 a house. A sewer hookup there costs $1,500. Sewerless composting toilets or aerobic systems cost from $1,500 to $2,000.

The new provisions may also become very important in future droughts, such as the one Fairfax County suffered last fall, or when additional moratoria are placed on building new sewer lines.

A second major development of recent months was the purchase by American Standard, Inc., a large manufacturer of plumbing fixtures, of the Cole Resdevel Corp., a small company in Flair Lawn, N.J., that has perfected a sewerless toilet system.

The Cole system relies on modern technology to solve mankind's age-old sanitation problems, by the use of electrolysis. Ordinary table salt is dissolved in fresh water in the commode, and each flush delivers two or three quarts of salty water.

Wastes are flushed to a tank where electrolytic action cleanses them and purifies the water, which is recirculated back to the toilet. This feature alone saves 30 to 40 percent of all fresh water piped into the typical home. No sludge is produced; the only residue is the sterilized toilet paper, which accumulates in a trap and must be removed about once every six months.

This electrolytic process can also be used to cleanse the "gray water" from the household; that is, wastewater from kitchen sink, washing machine, basins and bath.

With the new equipment in successful operation, no municipal water or sewer hookup would be needed.

The process was orignially designed for use in boats and mobile homes in order to by-pass the messy chore of dumping sludge at marinas and trailer parks, but American Standard intends to sell the new equipment for household use as well.

Plans call for production to begin within several months. No price has been announced but according to estimates the commode and related clean-up unit will cost no more than a first-class commode of conventional design. The gray water unit would be an extra.

The Cole toilet system was demonstrated last April for Fairfax County Board of Supervisors. A prototype unit was subsequently installed in a Fairfax County home but was removed last December when American Standard took over Colde Resdevel.

According to John Clayton, director of the county's Division of Environmental Health, the device needs additional work. He said the manufacturer had promised it would be odor-free and the water in the bowl would be crystal clear. In fact, the home experiment showed, when the toilet is not used frequently, the water tends to turn brown and odor develops, Clayton said.

John Herrity, chairman of the Board of Supervisors, said the company indicated that it planned to install an improved unit in the Fairfax home in the near future. Another will also be placed in a refuse dumping area, where it is expected to undergo concentrated testing.