Existing-home sales slumped 8 percent in September to their lowest level in nearly three years, the National Association of Realtors reported.

The employment cost index rose 1.4 percent in the third quarter and advanced 5.2 percent for the 12-month period ended in September, the Labor Department said. The index measures changes in wages, salaries and employee benefits.

Housing Resources Management, one of the nation's largest managers of government-subsidized housing, has declared bankruptcy and abandoned its projects. The filing was made last Thursday, the same day officials of the California company failed to win reversal of a HUD order that cited irregularities in the management operation and barred the firm from taking over any additional projects.

Public Citizen backtracked for a second time in a week from its critical study of the insurance industry, saying it had been wrong in saying that Aetna's property and casualty surpluses had declined. Last Friday, the consumer group admitted a similar mistake in its analysis of the ITT Hartford insurance group.

Philips, the Dutch electronics firm, plans to cut 35,000 to 45,000 jobs, or 12 percent to 16 percent of its work force, by the end of 1991 to boost productivity and survive Japanese competition.

The Wall Street Journal's newsstand price will rise by 50 percent to 75 cents a copy in December.