The government said yesterday that major labor contracts negotiated in the first nine months of this year provided for first-year wage increases averaging only 3.8 percent, not enough to keep up with the likely rate of inflation and less than half as much as the same unions won the last time around.

That figure is both good news and bad.

The bad is that working families may lose some buying power, and so be less able to help spend the economy out of the recession.

The good news has to do with inflation. In most industries, outlays for labor are a large part of the cost of production. The less they rise, the less upward pressure there is on prices. Many economists actually use labor costs as a measure of the underlying rate of inflation.

In any case, yesterday's figures were another indication of how powerfully the recession and unemployment are dampening wage increases across the economy.

So far in 1982, inflation is running at an annual rate of 4.8 percent. In no year since 1968 when the government first started tracking such settlements have first-year pay increases in major contracts been as low as 3.8 percent. In 1979 or 1980, when the same unions bargained the last time, the average increase was 8.3 percent.

Two-fifths of the 2.7 million workers covered by settlements reached during the period won no specified wage increases at all. Most of these are in the troubled auto and trucking industries, where settlements early this year included major wage and benefit concessions. Wages of some workers actually will decrease.

Nearly all these workers, however, are covered by cost-of-living adjustment provisions (not included in the basic wage figures above), which are tied to the Consumer Price Index.

As for wages already in effect, for all workers covered by major union contracts they rose an average 5.3 percent (including cost-of-living increases) in the first nine months of this year. This was the smallest rise since 1973, although it was enough to keep just ahead of inflation.

Some 8.5 million private sector workers are covered by such contracts.

In the depressed construction industry, where unemployment is approaching 20 percent, agreements showed the smallest nine-month increase since 1978. Here, wage settlements gave average first-year increases of 7 percent, compared with 11.3 percent the last time the parties bargained.

These figures might have been lower, except that most union construction work is on commercial office buildings or roads, which have not suffered the same hardships as the housing industry, according to a BLS analyst.

If those workers in troubled industries affected by a wage freeze are eliminated, the average first-year increases for the rest averaged a healthier 7.1 percent. Workers who will receive increases are in construction, apparel, electrical equipment, manufacturing and utilities industries.

The figures are "worker weighted," so that contracts involving more people are given more weight. Only those covering at least 1,000 were included.

The above figures do not include changes in fringe benefits. BLS figures for total wage and benefit packages (only for groups of at least 5,000 persons) in the first nine months of 1982 showed average first-year increases of 3.3 percent.