Bernard Tolbert, the former Buffalo FBI chief who has been exploring a mayoral candidacy for more than a year, said he will officially announce his candidacy Saturday.

His entry into the Democratic primary in September will take place Saturday morning in the Family Life Center of St. John Baptist Church, and it signals the start of a major challenge to incumbent Mayor Byron W. Brown, who is seeking a third term.

“I’ll be announcing on Saturday” is all Tolbert would say Wednesday.

Tolbert, who turns 65 this weekend, has been meeting for months with dozens of community leaders and attending virtually every civic event in town. He had never confirmed his candidacy until now, though it was all but certain he was in the race after he established a campaign finance committee and began raising money earlier this year.

Brown begins the race as the favorite, with more than $1.1 million in his campaign treasury and an experienced political organization ready to aid his efforts.

But Tolbert has promised he will raise enough money to prove a competitive opponent, and he has been quietly concentrating on fundraising for months.

In overwhelmingly Democratic Buffalo, it is expected that the Democratic primary will decide the next mayor.

But Brown has long cooperated with the Erie County Conservative Party, dating to the days when he served as an aide to former County Executive Dennis T. Gorski, who enjoyed Conservative backing. He is considered the favorite for the Conservative line, which usually does not attract many votes but would guarantee his appearance on the November general election ballot.

Conservative Party leaders are expected to interview Tolbert, Brown and Republican candidate Sergio R. Rodriguez on Tuesday, with an endorsement slated for later in the month.

Brown and Tolbert both intend to seek the Democratic Party endorsement.

Party Chairman Jeremy J. Zellner has indicated he would consider the mayor, despite Brown’s long estrangement from the party hierarchy.