A third challenger emerged Friday in the race to unseat Mayor John DeStefano Jr. in his bid for a record tenth term in office.

Former alderman Robert Lee, a Sikorsky Aircraft employee who lost his Ward 11 seat to Maureen O’Sullivan-Best in 2009, declared his candidacy at City Hall Friday afternoon. Reached by phone Friday evening, Lee said he would work to impose term limits for the mayor and aldermen, arguing that during his 18-year tenure, DeStefano has “lost sight” of New Haven residents.

“If the highest office in the country has a term limit, why not the mayor?” Lee said. “If it’s good enough for the president, it’s good enough for me,” Lee said.

Lee said he would limit mayoral terms to four or five. Beyond that, he said, a mayor becomes committed to too many different interests to be an effective advocate for city residents.

While he is a member of the Teamsters Union and will be seeking the endorsements of city unions, Lee said he would not base his candidacy on union issues. The past year has seen a bitter fight between city unions and the DeStefano administration over the proposed privatization of school custodial services and changes to city employee compensation packages.

“I won’t be trying to privatize the jobs of city employees, and I’m not for taking away things that people have worked hard to get, but I’m also not for pinching the taxpayers until it’s the last straw on the camel’s back,” Lee said.

What most compelled Lee to throw his hat in the ring, he said, was the need for “new ideas.” For example, he said, although DeStefano and the New Haven Police Department have been focusing on getting guns off city streets, the city’s crime strategy should also seek to prevent the flow of illegal weapons into the city.

By declaring his candidacy, Lee became the third African American candidate in the mayoral race — a fact that has drawn speculation among some supporters that black voters may split their votes and thus undermine the effort to defeat DeStefano. Clifton Graves, a civil rights activist and former city attorney, declared his bid April 19, and Tony Dawson, a former alderman from the Hill neighborhood, joined the race May 14.

Lee recently called both Dawson and Graves, he said, to discuss the possibility of an agreement under which only one of the three would run. While nothing came of the discussion, Lee said, he said he is “optimistic” about the prospect of such a deal and plans to call both candidates again soon.

“It’s not about the individual, it’s about the city,” Lee said.

For his part, though, Lee showed no intentions of stepping out of the race.

If he qualifies for the ballot and remains a candidate, Lee will be running in the Sept. 13 Democratic Primary.