A group of union activists set on ousting Transport Workers Union Local 100 President Roger Toussaint plans to kick off its campaign today by launching a slate of candidates, the Daily News has learned.

Toussaint took the 33,700 transit workers out on strike for three days last December and then summoned them back to work. The union still doesn't have a contract.

"He made a grave error," said Barry Roberts, the presidential candidate on the Rail & Bus United slate. "We were willing to stay out. He destroyed the workers' morale."

Roberts, a bus driver and the chairman of the local's Manhattan and Bronx division, is joined on the slate by track division chairman John Samuelsen and Nat Cummings, a conductor who has held several union posts in a third major union department, rapid transit operations.

The three said they wanted to bring democracy back to the local - accusing Toussaint of being an autocrat who undermines other union officials he sees as potential threats.

Several, including Samuelsen, have been fired from union staff positions for voicing opposition to Toussaint on union matters, they charged.

With the contract now in arbitration, Toussaint said he's committed to getting his members a fair pact and is planning a series of protests.

"We need to show strength on the ground," said Toussaint, who spent three days in jail for leading the illegal strike.

The union vote is set for December.