In June, when state Sen. Robert J. Garagiola (D-Montgomery) announced his resignation, leaders of the county’s minority communities saw it as an opportunity to breach a major political barrier.

For all of its much-celebrated progressive tradition, Montgomery County has never sent a candidate of color to the state Senate. Advocates had hoped that the county’s Democratic establishment would use the opening to add some diversity to the all-white, eight-member delegation.

Instead, the process of filling western Montgomery’s District 15 seat has exposed long-simmering tensions in a county transformed by rapid demographic change. Although the opening is only for the balance of an unexpired term that will end after the 2014 elections, it has become a rallying point for an ambitious immigrant political class seeking to convert economic success into access to elective office.

“The delegation doesn’t look like the county looks,” said Karen Britto, who formerly chaired the county’s Democratic Central Committee.

Montgomery is a “majority-minority” jurisdiction; 48 percent of the county’s 1 million residents are white, according to 2012 Census Bureau estimates. But just 13, or 24.5 percent, of 53 elective offices in the county are held by minorities: seven of 24 state delegates, three of nine County Council members, two Board of Education members (an eighth, student member is elected by students only) and County Executive Isiah Leggett (D).

The county’s Democratic Central Committee has scheduled a Sept. 10 vote on a recommendation to Gov. Martin O’Malley (D), who will make the appointment. But within days of Garagiola’s June 5 announcement, most of Montgomery’s Democratic leadership, including Leggett, closed ranks behind Del. Brian J. Feldman (D-Montgomery), a white three-term incumbent and one of District 15’s three state delegates.

What especially vexed minorities was an announcement by the District 15 Democratic Caucus — the core group of active Democrats in that area — that it had endorsed Feldman. In fact, only the caucus’s executive committee had agreed to support Feldman.

“If you have a caucus, you ought to caucus,” said Jason Tai, an Asian American lobbyist and Potomac resident of District 15, who likened the process to old-style Chicago politics.

“There are tens of thousands of registered Democrats, and this was the first I’d heard about the caucus supporting a particular Democrat,” he said.

Timothy Whitehouse, the caucus co-chairman, said the announcement should have made more clear that it was expressing only the position of the group’s leadership. But he said he was comfortable with the endorsement of Feldman, calling him an effective and popular legislator.

He added: “There will be an election coming up next year, so the caucus leadership felt it would be a mistake to appoint someone who had not been an elected official.”

But to Britto and other Democrats, the automatic movement toward Feldman felt like a business-as-usual anointment that ignored the county’s altered demographic landscape.

It sparked a series of meetings in recent weeks, including one Wednesday at which Latino, Asian, African American and Arab American community representatives — nearly all longtime supporters of Leggett’s — urged the county executive to support a more open and deliberate process.

The group — which includes Britto, council member Valerie Ervin (D-Eastern County), the council president, Nancy Navarro (D-Midcounty), and Stan Tsai, chairman of the Chinese Culture and Community Service Center — told Leggett that they plan to press the central committee to bypass Feldman and name a “caretaker” who would not run for Garagiola’s seat next year. This would allow time, they said, to find a more diverse field of candidates to compete in an open primary in June.

“It will create the opportunity for a fair and open primary process,” said Gustavo Torres, the executive director of CASA of Maryland, who was speaking for CASA’s political arm, CASA in Action.

Torres said the group had asked Bilal Ayyub, a University of Maryland engineering professor and a member of the Governor’s Commission on Middle Eastern Affairs, to submit his name to the central committee for consideration as the caretaker. Ayyub, 55, a District 15 resident born on the then-Jordanian West Bank, declined to comment Friday. Leggett did not respond to a phone message.

Some Democrats who support Feldman are offended by what they see as the blatantly racial calculus employed by Britto and her group. They believe that Feldman has been unfairly penalized for the color of his skin.

Council member George L. Leventhal (D-At Large), a former central committee chairman, said he unconditionally shares the goal of diversifying Montgomery’s political leadership. “At the same time,” he said, “we’re not going to have an absolute rule that no white people need apply.”

Others observers argue that District 15, a swath of western Montgomery stretching from Hyattstown to parts of Potomac, is not the ideal place to attempt to break the white dominance of the Senate delegation. It has a minority population of about 40 percent, with Asians (22 percent) as the largest subgroup. Five other county legislative districts have higher-percentage minority populations. Those observers also point out that it wasn’t that long ago that the district was electing Republicans — the last one, Del. Jean Cryor, was defeated by Democrat Craig L. Rice (now County Council vice president) in 2006 — and that caution is in order.

Britto said the numbers are misleading because Arab Americans are counted as white in census data. In any event, she said, “the opportunity is in 15, and the opportunity is now,” she said.

Gabriel Albornoz, executive director of the central committee, said the organization has done nothing to inhibit anyone from asking to be considered for Garagiola’s seat.

“The committee stands ready to fully vet and interview all prospective candidates,” said Albornoz, who also serves Leggett as director of the county Recreation Department.

Feldman, 52, a former Justice Department trial lawyer who litigated tax cases, is chairman of the county’s House delegation. Among the bills he sponsored and helped pass was legislation establishing economic sanctions for electric utilities that fail to meet reliability standards.

He has been quietly visiting with groups of central committee members to build support. He said he is not disturbed to find himself at the center of an intraparty fight over diversity.

“I think it’s a legitimate discussion to have for the county and a healthy conversation to have,” he said. He added that in recent weeks the focus has been “much more on my qualifications for this seat and my ability to step in on day one.”

This article has been corrected to say that Del. Brian Feldman is the former chairman of the Montgomery House Delegation. Del. Anne Kaiser is the current chairwoman.