First-year wage increases rose sharply during the first six months of 1981 as unions turned away from cost-of-living protection in favor of immediate cash, according to a report released yesterday by the Bureau of Labor Statistics.

Major bargaining units, those representing 1,000 or more workers, won first-year pay settlements averaging 11.3 percent between January and June, compared to 9.5 percent for the same period last year. Basic pay increases over the life of major contracts negotiated in the first half of 1981 averaged 9.2 percent, 1.2 points higher than overall contract pay raises won in 1980, the BLS report said.

The construction industry led the way in settlements, bestowing on its workers first-year increases of 13 percent and overall contract raises of 10.9 percent.

Contracts negotiated so far this year will last about 31.2 months, about the same as those negotiated last year, according to the report.

The substantially larger wage settlements are coming in the third year -- usually the lightest negotiating period -- of the three-year, national collective bargaining cycle. Heavy bargaining resumes next year with the start of a new three-year cycle involving unions in the auto, electrical, garment, meat packing, petroleum, rubber and trucking industries. Current contract settlement rates could greatly influence labor's demands in those talks.

However, Rudolph A. Oswald, director of economic research for the AFL-CIO, said yesterday that the wages won so far this year are in line with the kinds of contracts being negotiated.

"The reason why the change in wage rates seems so high is because you have more people this year who COLA (cost of living allowance) clauses," Oswald said. Cola clauses are designed to help workers recoup part of their purchasing power diminished by inflation. Unions signing contracts without a COLA tend to demand a higher base pay for their members, Oswald said.

The BLS figures released yesterday seem to support his argument.