Mellowed by Wednesday's 17-hour session and facing a bitter dues-increase fight tomorrow, delegates to the American Federation of Government Employees convention spent most of today taking care of important union constitutional questions.

The major item they resolved was a push from backers of newly elected executive Vice President John Sturdivant of Winchester, Va., to give him reponsibility for important union duties now in the hands of President Ken Blaylock.

At the urging of Sturdivant, now the highest-ranking black in the 225,000-member federal union, delegates voted to defer for two years a decision on whether to give him control of labor-management, contract and health and safety matters.

Sturdivant, who got more votes than either Blaylock or Secretary-Treasurer Nick Nolan, both of whom were reelected, asked delegates not to precipitate a "turf fight" over duties between himself and the union's president.

Sturdivant said "Ken and I have talked about the problems" of responsibilities and "we are going back to Washington to work them out. Give us a chance . . . without making us fight over turf."

Sturdivant said that if he is frozen out of AFGE's decision making, "I will be back in two years at the next convention supporting the resolution" designed to give him defined duties.

What could have turned into an ugly political division was headed off when most backers of the expanded role for the executive vice president then voted against their own motion.

Late Wednesday evening, delegates reelected attorney Barbara Hutchison to head the union's Women's Department. She got 148,973 votes to 56,028 for Denise Osborne.

Several Labor Department officials from Washington have been monitoring all facets of elections of AFGE national officers -- including the selection of many of the 1,200-plus delegates here -- since the beginning of the year.

Carl K. Sadler, the union's former legislative chief who lost to Blaylock two years ago in Honolulu (and again this week), said, and Labor agreed, that many of the delegates to the 1980 convention were chosen improperly. No election charges have been filed so far concerning the just-completed election.

Tomorrow, the delegates will vote whether to raise dues (now averaging between $6 and $8 per month) over the next two years to give Blaylock the tools to organize and get more involved in political campaigns.

The maximum increase being proposed would boost per capita dues (payments to the AFGE national office) by about $1.35 a month over the next two years. Dues increase battles are always tough in unions, but particularly so with federal and postal unionists whose dues are usually much lower than those of union members in the private sector.

Many delegates here favor a rise in dues, but they want to be sure that more of the money is returned to locals rather than kept in Washington. Because of the passions that dues increases always arouse, unions typically leave them until the last order of business.