The government next week is expected to announce a 4 percent raise for its 22,000 blue-collar workers here even though pay for similar craft and trade jobs in the private sector is up an average of 6 percent.

When officially approved, the adjustment will become effective Oct. 17 for most of the carpenters, mechanics, laborers and other craft and trades workers located mainly in the Defense Department and the General Services Administration.

The 4 percent pay raise is the same as that approved earlier this month for metro Washington's 300,000 white-collar employes who were also due a larger catchup-with-industry increase, according to the government's own data.

Defense officials say the 4 percent blue-collar raise would bring the average non-supervisory employe's salary up to $17,825. The average white collar civil servant here gets more than $26,000 a year.

Last year Congress and the White House limited white-collar and blue-collar federal pay raises to 4.8 percent.

Pay for the government's half million blue-collar workers is supposed to be linked to hometown private craft and trades salaries. The government has 140 geographic wage areas, metro Washington being one of them, where it surveys private industry pay. Defense made the survey here in August, and found that blue-collar pay in the metro Washington area was up an average of 6 percent over August 1981.

But because of a congressional limit on blue-collar federal raises (the same limit President Reagan imposed on white-collar U.S. workers), the raise will be held to 4 percent. It will work out to about $686 a year for the average blue-collar worker.

Blue-collar workers getting the raise include 5,000 employed by Navy; 4,000 with the Army; 1,200 Air Force employes; 4,000 with General Services Administration; 2,800 with Health and Human Services and about 1,000 in Interior. The Smithsonian has 800 workers who will get the raise; Commerce and Agriculture nearly 600 each and Department of Transportation 450.

The government next week is also expected to announce pay raises for several thousand employes here covered by the so-called lithographic wage scale.