Nelson A. Diaz, a former judge and Philadelphia city solicitor, will announce his bid for mayor in mid-January, according to a close adviser.

His entrance will bring the Democratic field to five - and make it the first time in modern memory that the list of viable candidates includes two Latinos.

Diaz, 67, will focus on education, said Elliot Curson, a veteran political advertising consultant who has been advising Diaz as he weighed a run over the last several months.

"He just feels that's the answer," Curson said Friday. "He feels that a better-educated city, better education among all populations, it makes a city a more attractive place to be."

Diaz, whose decision was first reported by WHYY 91FM, could not be reached for comment Friday. Curson said Diaz's tentative plan was to formally announce his campaign Jan. 15.

The declared candidates in next May's all-important Democratic primary are former District Attorney Lynne M. Abraham; State Sen. Anthony Hardy Williams; a former head of the city's Redevelopment Authority, Terry Gillen; and former City Solicitor Ken Trujillo, who also is Hispanic.

Word of Diaz's impending announcement was fodder for Friday evening conversation at the annual Pennsylvania Society gathering in New York City. Abraham, among numerous politicians in attendance, said Diaz had told her of his intentions.

Her take: "The more, the merrier."

Diaz grew up in the Harlem section of New York City and moved to Philadelphia to attend Temple University Law School, where he formed the first student organization for black and Hispanic students.

He boasts of having been the first Latino judge elected in Pennsylvania history, serving on Common Pleas Court from 1981 through 1993. He was city solicitor under Mayor John F. Street from 2001 to 2004.

He also was an aide to Vice President Walter F. Mondale, and was counsel to the Department of Housing and Urban Development in the Clinton administration. Diaz is now a partner at the Dilworth Paxson law firm and serves on the board of trustees at Temple University.

Curson said others had told Diaz his experience would make him a shoo-in for a City Council seat. But he said Diaz thought he could not accomplish his goals there.

He said Diaz had been considering a run for mayor for years and did not worry about the declared candidates when making his decision.

But Larry Ceisler, another local political consultant, said potential candidates can still be persuaded to run because the race is still wide open.

"People like Nelson Diaz, they look at the field and they say, 'Why not me?' " Ceisler said Friday.

Randall M. Miller, a St. Joseph's University historian and expert on the region's politics, said he, too, suspected Diaz assessed the field before deciding, and perhaps sized himself up against one candidate in particular - Trujillo.

"Part of it has to be, even if it was just subliminal, thinking about who should be, quote, the Latino candidate," Miller said. "And, 'It ought to be me, not Trujillo.' "

While the Latino vote traditionally has not been a major or unified power bloc in Philadelphia politics, and is known for the same low turnouts that characterize plenty of other city voting blocs, especially in nonpresidential primaries, Miller said both Diaz and Trujillo were likely hoping those voters can provide them with a base.

"I'd be surprised if there wasn't an uptick - if not a significant uptick - in interest in the mayoral race," Miller said. "There will be a conscious effort to reach that base and develop that base."

tnadolny@phillynews.com

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@TriciaNadolny

Inquirer staff writer Claudia Vargas contributed to this article.