Near-completion of a year-old project to decrease pollution due to unsanitary sewage disposal in the Charles River was announced yesterday by Clarence I. Stirling, Chief Sanitation Engineer of the Boston Public Health Commission.

The Charles, an evil-smelling, unappetizing body of water that separates Soldiers Field from Jim Cronin's, will never become a swimmer's paradise, nor has its density any prospects of improving, since there is no way in which the flow of sewage from upstream factories, mills, and laundries can be diverted.

However, according to Worthen H. Taylor, Senior Sanitation Engineer for the Commission, the chlorination of waste products at the sewage treatment plants, which is the most important accomplishment of the project, will drastically reduce the potentially dangerous bacterial pollution which has always been a threatening factor to the health of Cantabrigians.

Clearing up the 60-odd miles of the Charles, which passes through the heart of Massachusetts' most heavily populated and highly industrialized areas has been a State House headache since the turn of the century. The underground pipes which lead from the treatment plants to the river were intended for a much lighter load than the present one.

Another complicating factor is the fact that one-third of the river's flow is diverted into the Neponset River through the 300-year-old Motherbrook Canal, with the result that as much as 15,000,000 gallons a day have to be pumped into the river to dilute the flow of sewage when it becomes too heavy.

Instead of working at the hopeless task of making the Charles suitable for swimming, the Commission is construct- ing a series of public pools on the river's banks. Another constructive step which has been taken is the lessening of waste production in the woolen mills through the adoption of improved industrial techniques. But, Mr. Taylor states, this is only a minor triumph. "The sheep is a filthy animal," he says, and nothing can be done about it