Supporters of Mayor Harold Washington won two aldermanic runoff elections tonight, giving him his first chance since his election three years ago to take control of Chicago's racially divided City Council.

Alderman Edward R. Vrdolyak, the mayor's arch-rival on the council, conceded that the mayor's candidates had won the special elections in the 26th and 15th wards. In a statement read by a spokesman, Vrdolyak said, "The mayor has achieved his goal of 25 votes in the City Council.

"We stand ready to work with [Washington] and his council supporters on programs that will benefit and move the city ahead," Vrdolyak said, adding, "We reserve the right to disagree with him when he is wrong."

In the 26th Ward, with 41 of 44 precincts reported, unofficial returns showed Washington-backed candidate Luis Gutierrez had 6,861 votes, or 54 percent, to 5,893 votes, or 46 percent, for Manuel Torres, a Cook County board member aligned with Vrdolyak.

In the 15th Ward, with all 55 precincts counted, unofficial returns showed black activist Marlene C. Carter had 10,463 votes, or 65 percent, to 5,525 votes, or 35 percent, for Alderman Frank J. Brady, a member of Vrdolyak's majority bloc of whites on the council.

The victories by the mayor's allies will give Washington backers 25 seats on the 50-member council, with Vrdolyak supporters holding the other 25. Washington, however, will now cast the tie-breaking vote.

Control of the council would allow the mayor to move on dozens of appointments to boards and commissions long stalled by Vrdolyak, the chairman of the Cook County Democratic Committee. Vrdolyak controlled 29 council votes until special elections last month in wards redrawn to enhance minority representation.

Today's ward contests were runoffs scheduled when no candidate took a clear majority in last month's elections.

The 26th Ward race was expected to be the toughest battle, and aldermen, party committeemen and political organizers from both sides have blanketed the heavily Puerto Rican area over the last few days to get out the vote for Gutierrez or Torres.

Torres' advisers worried today about an election-eve debate on Chicago's Spanish-language television station, Channel 44.

In Monday night's debate, Torres spoke Spanish for about 10 minutes, then switched to English. Gutierrez has long accused him of speaking Spanish poorly, and Torres' performance on the program became the major issue between the two.

Torres, born in Puerto Rico, moved here as a child and acknowledged Monday night that his English is superior to his Spanish.