The state of Maryland yesterday lifted its seven-year-old moratorium on new sewer connections in much of eastern Prince George's County, opening a 110-square mile area to a wave of development that has been prevented since 1970.

The decision announced by Maryland's Secretary of Health Neil Solomon was prompted by the expansion of the wastewater treatment plant in the southeastern area of the county, which doubles sewage treatment capacity in the large Western Branch drainage basin.

This newly available capacity could result in the construction of some 10,000 homes in the area over the next three years, but county planners estimate that the dynamics of the housing market should hold that total down to about 3,000 units.

Even this more conservative growth estimate would mean an additional 9,000 people moving into an area that includes Greenbelt, Largo and Upper Marlboro by 1980.

If construction at the plant goes according to schedule, the capacity of the Western Branch waste water treatment plant will double again by the fall of 1978, from the 15 million gallons a day of capacity now available to a total of 30 mgd., further accelerating the potential for growth.

Yesterday's sewer moratorium end takes the Washington area one step further away from the era of retrenchment and slow growth that followed the boom years of the 1960s.

During that decade of helter-skelter development, the pace of construction often far outran the capacity of local governments to provide such essential services as sewers.

Moratoriums on new sewer hookups were first declared in large areas of Prince George's and Montgomery counties when overflows at sewage treatment plants became "almost daily occurences," according to Earl Quance of the state health department.

When local governments failed to act to relieve the problems, Quance said, the state moved in.

About 250 square miles of suburban Maryland still remain under complete or partial sewer moratoriums many of these restrictions are expected to ease before long, as new treatment facilities become available.

The last sewer moratorium in Fairfax County in Virginia was lifted more than two years ago, and sewage treatment capacity is expanding there, making it the growth center of the metropolitan areas.

"No one likes sewage restrictions," Maryland Health Secretary Solomon said yesterday in announcing the end of the Western Branch moratorium.

"But the use of such authority is sometimes the only way we can protect the public health at the same time making certain that development occurs in pace with the provision of sewage treatment facilities.

"It is the responsibility of local governments to assure that development is not allowed to exceed available sewage treatment capacity," Solomon added.

With the new addition of 7 million gallons a day to its total capacity, the Western Branch treatment plant will finally be able to serve some developers who have waited as long as 10 years for sewer allocations.

Last year, however, the Prince George's County Council approved County Executive Winfield M. Kelly's pland to use sewer allocations as a tool to shape the king of development that will occur. Under a new law, residential construction will be favored over commercial development, and single-family homes over apartments.

The opening of the expanded sewer treatment plant gives county planners their first chance to put this new policy into effect.

According to the Kelly plan, which no developer has yet challenged in court, 80 per cent of the new sewer hookups will be given to residential developers and 20 per cent to commercial construction.

Beyond that, 47 per cent of the residential construction must be single-family homes, 44 per cent town houses, and only 9 per cent of the treatment capacity allocated to residences may be used to build apartments.

In this way, Kelly who has long bemoaned his county's image as a concrete sea of apartments, hopes to encourage more junior executive-style developments like Kettering, Enterprise Estates and North Hampton.

All three of these developments are in the Western Branch drainage area, and all are expected to expand now that the sewer moratorium has been lifted.

Ken Duncan, administratior for the Prince George's County Council, said yesterday a list of those developers who have applied for capacity was drawn up a year ago, and the sewage allocations will be granted on a first-come, first-served basis - subject to the overall Kelly formula.

Duncan cautioned that, if developer fails to make progress toward finishing construction and using his capacity within a year or so, the county may take it back and give it to someone else.