The fiercest state legislative contest expected in Western New York this year kicked off Thursday when City Hall fixture Michael Kuzma declared his candidacy against Sen. William T. Stachowski in the September Democratic primary.

County Legislator Timothy M. Kennedy of South Buffalo joins the race this evening when he declares during a fundraising event at the Iron Workers Hall in West Seneca. Attorney Sean Cooney of Buffalo also is expected to join the race, along with Thomas P. Casey of Orchard Park, who previously ran against Republican Sen. Dale M. Volker of Depew.

Other potential challengers include County Legislator Daniel M. Kozub of Lackawanna, Lackawanna Mayor Norman L. Polanski, Cheektowaga Councilman James Rogowski and attorney Dennis C. Gaughan of Hamburg.

It all adds up to a robust challenge within his own party to Stachowski of Lake View, who has served in the Senate since 1981. While other candidates also could emerge if Stachowski were to retire, the senator made it clear in a recent letter to Democratic committee members that he has no such intention.

In the letter, he seemed to establish a theme that will guide his campaign. He will emphasize, he said, that he is a Democrat who did not join last summer’s coup that temporarily ousted the Democrats from power in the State Senate.

“Back in June, during the height of the tumult in Albany, I was pressured to switch parties under the guise of ‘good government,’ ” Stachowski wrote. “But I remained true to my roots, and to my commitment to the residents of the 58th Senate District who elected a Democrat to represent them in Albany.”

Kuzma, senior legislative assistant to Common Council President David A. Franczyk and an unsuccessful candidate for Buffalo city judge in 2003, officially joined the race during an event for friends and supporters at the First Amendment Club, 93 Bridgeman St.

He has said he will run a “left of center” campaign for the post, hoping for success in what is proving a crowded field. He listed on his campaign announcement his lifetime membership in the Eugene V. Debs Foundation, named for the famed Socialist of a century ago who ran for president five times.

“We’ll be talking about a lot of issues the other candidates won’t raise or will only sidestep,” Kuzma said. “For example, I fully support same-sex marriage. I support term limits after eight years, and I will honor all Indian treaties.”

Kuzma also said he will support previous resolutions introduced in the Senate calling for the withdrawal of all New York National Guard units from Iraq and Afghanistan.

While Kuzma is not expected to report a brimming campaign treasury when he submits financial reports to the state Board of Elections next week, Kennedy said he will have about $100,000 on hand. He is expected to draw a sizable crowd to his event tonight, reflecting the substantial support he anticipates receiving from top Democrats like Rep. Brian Higgins, D-Buffalo.

“This is about changing the way Albany functions on behalf of Western New York,” he said Thursday in a preview of his speech. “We’re sick and tired of being treated as second-class citizens. I’m ready to go to Albany and take on the status quo.”

Kennedy also said he is eager to tackle issues like Medicaid reform to reduce the tax burden on property and business owners.

While Kennedy anticipates support from Higgins and other party figures, Erie County Democratic Chairman Leonard R. Lenihan is expected to stick with Stachowski.