Kenneth T. Blaylock, a 47-year-old plumber on leave from his civilian Air Force job, today was elected to a fourth term as president of the American Federation of Government Employees union.

Blaylock, a member of the AFL-CIO executive council who promised to steer a more political course for the U.S. worker union, beat Carl K. Sadler by 120,529 to 48,187.

The 1,200-plus delegates at the 50th anniversary convention of AFGE voted in less than two hours this morning, but had to wait most of the day for the explosion that came when national vice president Royal Sims of Philadelphia announced the results.

The Blaylock-Sadler contest was a rematch of a slugfest the two had in Honolulu in 1980 when Sadler ran a closer race against Blaylock, who was closely identified with the Carter administration, which then was unpopular with federal workers.

Sadler protested that many delegates to the Hawaii convention had been selected improperly, and the Labor Department agreed to supervise delegate selection for 1982 and to keep an eagle-eye on the current convention.

Labor Department observers have been on hand -- at AFGE headquarters and in field locals -- observing local elections of delegates who vote in the name of AFGE's 225,000 due-paying members. In the process, Labor Department officials edited every line of the union's newspaper, and even screened -- for political content -- a film shown to delegates earlier this week.

Nicholas Nolan, of Baltimore, the union's secretary-treasurer ran a strong race defeating William Nussbaum by 110,747 to 77,435. Norm Fischer, a civilian employe of the Air Force in Washington, got 16,923 votes.

A runoff was under way today between two men in the crowded, eight-man race for the No. 2 office of national executive vice president. (Wayne Buckle, a former AFGE staffer, was appointed to fill the office on an interim basis after the death earlier this year of Joseph Gleason).

In the runoff were John Sturdivant, who got 82,874 votes, and Allen Kaplan, with 36,107. Kaplan is a national vice president from the Chicago region. If elected, Sturdivant would be one of the highest ranking black officers in the labor movement. He formerly was president of an AFGE Defense Department local in Winchester, Va., and worked as a paid staffer at the union before resigning to campaign.

Walter F. Peters, a national vice president from California got 30,361 votes, too few to qualify him for the runoff. Ralph Fitch, the national vice president for Maryland, Virginia, West Virginia and North Carolina, ran fourth with 25,923 votes.

Blaylock's political fortunes have increased as the Reagan administration tightened its budgetary screws on federal workers. After the 1980 election, Blaylock chided members -- via the union's newspapers -- who voted for "the forces of darkness and reaction," that is, Ronald Reagan. It is estimated that 60 percent of AFGE's members voted for Reagan but it is clear from this convention that is not likely to happen in 1984.

This convention is expected to give Blaylock approval to be more active in political campaigns, with emphasis on trying to dump Republican members of the House from big federal employe districts (like Frank Wolf and Stan Parris) in favor of Democrats who will promise to block future attacks on federal pay, pensions and increased use of contractors.

He reportedly has been assigned to target Sen. Orrin Hatch (R-Utah) for defeat. Because of big membership at Hill AFB and the federal employment centers in Salt Lake City and Ogden, AFGE is one of the largest unions in Hatch's home state.

Blaylock has made it clear he plans to pump union political funds into the campaign of friendly (mostly Democratic) congressional candidates.

On Thursday, Blaylock hopes to tranform his Labor-Department-seal-of-approval election mandate into clout that will enable him to get a 50-cent-per-month dues increase for AFGE members -- who now pay between $6 to $8 per month in local and national dues -- this January.