Mayor Marion Barry called on several hundred of his supporters yesterday to join him in a "crusade" to win an at-large D.C. Council seat this fall, and said he would campaign as the "constituent ombudsman" for voters in Ward 3 and other parts of Washington where he is weakest politically.

"I'm going to win," Barry told reporters after a breakfast meeting with dozens of his political lieutenants, who face the challenge of turning out the mayor's still considerable base support in the Nov. 6 election. Six candidates are competing for two at-large council seats. The top two vote-getters will win the seats.

Barry, who in the aftermath of his cocaine possession conviction was advised by some associates against running for a council seat, said his campaign was "on track," and vowed to take his message to each of the city's 140 precincts.

Barry, a longtime Democrat who quit the party this summer to run for council as an independent, warned his supporters not to be "lackadaisical" about the election. "It's going to have to be a crusade," the mayor said, "a crusade on your job, off your job, in your church, wherever you are, 24 hours a day, for Marion Barry."

Some of Barry's staunchest allies said that while the mayor has a good shot at winning, the race will be a difficult one, in part because of the untraditional quality of a campaign outside the city's ruling Democratic establishment. They also said the mayoral primary victory of Democrat Sharon Pratt Dixon, who had campaigned against city hall, reflected a political climate not altogether hospitable to Barry, who has presided over the District Building for nearly 12 years.

Barry sought yesterday to rally troops disheartened by Dixon's win, saying, "The election's over. It's gone. You can't undo the results."

The mayor also portrayed himself as a friend of city government employees. Dixon has pledged to fire 2,000 of them if she succeeds Barry.

"Now, we may have some employees that don't carry their weight, but the great majority of D.C. government employees work hard," Barry told the crowd, which included some civil servants.

Barry campaign manager Anita Bonds told the crowd that the Hatch Act ban on city workers' engaging in partisan political activity after working hours does not apply to the mayor's supporters because he is no longer affiliated with a party. Bonds said that a key part of Barry's electoral machinery -- a phone bank to identify his voters around town -- will begin operating Tuesday.

In remarks to supporters gathered at a meeting room at the Robert F. Kennedy Memorial Stadium Complex, Barry said he had been rejuvenated after 244 days of sobriety and a court verdict that, while mixed, was not as bad as it could have been. "If we can make it through that trial, we can make it to city council," Barry said.

He said a campaign was a natural part of his recovery from substance abuse. "In recovery, you've got to have a meaningful life ahead of you."

Paul Kuntzler, a Southwest resident who worked in Barry's first mayoral victory in 1978, said that with the mayor so weak politically among whites, "it's going to come down to how strong he does in the black community."

"It's going to be tough" garnering support among whites, said Kuntzler, who is white. "But we should compete for that support. Any meaningful bloc could make a big difference."

Barry's opponents include Ward 4 school board member Linda W. Cropp, the Democratic nominee; W. Cardell Shelton, the Republican nominee; council incumbent Hilda H.M. Mason (Statehood-At Large); and independents Ray Browne and Clarene Martin.