A government barometer future economic trends showed a healthy increase for the third straight month in October, the Commerce Department said yesterday.

The one-half percent increase in the index of leading indicators was a sign that the economy is continuing to grow at a steady rate.

A decline in the indicators for several months could mean an economic downturn and higher unemployment.

The government is trying to slow economic growth slightly in its fight against inflation, but results of its credit-tightening moves may not show up until next year.

The 0.5 percent gain in October followed back-to-back increases of 0.9 percent in August and September. The department originally had reported the September increase as 0.7 percent but revised it upward.

The main reasons for both the September and October increases were rising demand by businesses for plants and equipment. That is considered a sign of business confidence and means businesses will continue to produce.

Also contributing to the October increase were a rising average work week, deliveries, liquid assets and orders received by factories.

Negative contributors were a higher layoff rate, sensitive prices, falling stock prices, a decline in the money supply and fewer building permits.

The index stood at 139.2, meaning that these indicators had grown by 39.2 percent since the base period of 1967.