The "average" families in Prince George's and Montgomery counties will pay about $17.33 more in water and sewer charges next year as a result of a budget approved by the two county councils late last night.

The councils met in Upper Marlboro to conduct the annual ritual of reconciling the differences in their respective budget proposals for the two bicounty agencies that oversee water and sewer service and planning, parks and recreation. Since the two sides could not agree on many major items, the original proposals submitted by the agencies were adopted.

The major disagreement between the proposals for the budgets for the fiscal year that begins July 1 was over cost-of-living raises for the 2,000 employes of the Washington Suburban Sanitary Commission and the 750 employes on the Prince George's side of the Maryland-National Capital Park and Planning Commission. The Montgomery council had approved a 4.8 percent raise, while the Prince George's council had voted against any increase, citing budget constraints. Since the two sides could not agree, the employes will receive the 3 percent raise originally proposed by both commissions.

Prince George's council member William Amonett said layoffs will result among park and planning employes in his county, since the County Council has already voted to delete funds for any raises. Amonett said the number of layoffs or the size of program cutbacks could not be determined last night.

The councils approved a $390 million budget for the WSSC that includes a combined water and sewer rate increase of about 6.5 percent. For the family of four that uses 100,000 gallons of water each year, the bill will rise from about $254 to about $271 next year. Montgomery officials had proposed an increase of 12 percent, saying that the agency has been using an accounting practice that is delaying a deficit. But the Prince George's council would not go along.

The councils made only minor adjustments to the $31.8 million park and planning budget, with both sides agreeing to cut about $15,000 worth of administrative expenses.