A government index designed to predict future economic activity rose 0.5 percent in April, confirming projections that the economy will rebound sharply from the bad winter.

The Commerce Department reported yesterday that the most important contribution to the rise in its index of leading economic indicators was a 0.4 percent rise in the money supply.

The Federal Reserve Board, the nation's central bank, has taken steps in recent weeks, however, to try to restrain money growth because it fears that too fast growth will spur inflation, which has been accelerating in recent months to near the double-digit level.

In a related development, the administration's Council on Wage and Price Stability blasted a series of settlements between electrical workers and contractors in San Francisco as "highly inflationary and out of line with efforts to decelerate the rate of inflation."

The council, which functions as the administration's inflation monitor, said that the settlements ranged from 9.5 percent to 11 percent in the first year and from 20 to 22 percent over two years.

"They represent the largest hourly increases won by any construction workers this year, and are nearly double the national average for any such increases."

Officials of the council had tried to convince the locals of the International Brotherhood of Electrical Workers and the contractors to show some restraint in the bargaining process, but were rebuffed.

In the statement released vesterday, the council noted that the large increases "come on top of hourly wage and benefit packages that already average over $17."

But the President's program to convince business and labor to moderate their wage and price demands got some good news yesterday too, when Aetna Life & Casualty promised to hold pay increases for its top executives to 5 percent over the next 12 months.

The pledge applies to 65 top officials of the Hartford-based insurance company. Other major companies which have pledged to follow the administration's suggestions on hoding down executive salaries include General Motors Corp and American Telephone and Telegraph.

"We're doing it because it's the proper thing to do," an Aetna spokesman said. "We're trying to help the administration control inflation."

Robert S. Strauss, the top presidential adviser on inflation, praised the Aetna action and said it was valuable in "chipping away" at inflation.

Aetna is the first financial company to announce compliance with the President's suggested guidelines on executive pay.

The 0.5 percent rise in the index of leading economic indicators follows a 0.1 percent decline in March.

Most government and private analysts expect the economy to grow sharply - in the to 10 percent range - during the second quarter after a slight decline in real gross national product in the first quarter. Analysts blame the first quarter decline on bad weather and the coal strike and say about half the second quarter increase will represent sales and production that were missed in the first quarter.

The Council on Wage and Price Stability, in a separate report, said that in the coal settlement reached in late March, miners received pay and benefit increases averaging about 36.8 percent even though output per miner has been declining steadily in recent years.

The council has already called the coal pact inflationary and worried that it might set a precedent for other labor contracts due to negotiated this year and next.