Mayor Vincent C. Gray’s loss in Tuesday’s Democratic primary, combined with the possibility that nearly one-fourth of the D.C. Council could turn over next year, has inaugurated an unprecedented nine-month period of political upheaval in the John A. Wilson Building.

Gray will kick off his extended stint as lame duck Thursday morning, when he presents his final budget to lawmakers. He will preside over the city for only the first three months of the coming budget cycle, with the rest left to the victor of November’s general election, who will be sworn in Jan. 2.

Two of the sitting council members tasked with hammering out the spending plan are favorites to succeed Gray — Muriel Bowser (Ward 4), the Democratic nominee, and David A. Catania (At Large), a declared independent challenger.

In her first question-and-answer session with reporters after her primary victory, Bowser suggested that because she would “live with it” as mayor, she intends to take an outsize role in shaping the budget.

“I will dig into it deeply,” she said of Gray's pending proposal, “and I will work with my colleagues on the council to make sure there are priorities that I can support when I get in office.”

D.C. Council member Muriel Bowser captured the Democratic nomination for D.C. mayor on Tuesday. PostTV talks to her supporters and Mayor Gray's defenders about what the city would look like under a Bowser administration. (Theresa Poulson and Gabe Silverman/The Washington Post)

Others on the council dais are bracing for more internal discord even after a primary election season in which four members were seeking the Democratic nomination for mayor. And with Bowser making overt calls for party unity Wednesday as she braces for the fall election, the budget battles could take on a rare partisan tinge.

Council member Anita D. Bonds (At Large), who also serves as chairwoman of the D.C. Democratic Party, said the next few months could be “hell” in the Wilson Building. “It won’t be as smooth as people want to see,” she said. “There will be some ups and downs.”

Already much is known about Gray’s budget plan because of initiatives he unveiled during the campaign season: a plan to spend $300 million on a new Ward 8 hospital, a $116 million commitment to new education funding and a new parental leave program for city employees.

Other matters remain in suspense: which elements will he adopt of an ambitious tax reform plan developed by a blue-ribbon commission and whether he will propose devoting some $20 million to implement a scholarship program favored by Catania.

Gray stayed out of public view Wednesday, canceling a planned evening appearance at a community meeting and resting after a multi-day campaign sprint and an unusually late ballot count, according to spokesman Pedro Ribeiro.

The mayor’s top aides sought to assure residents that the administration’s commitment to delivering city services would continue unabated despite his rejection at the polls.

Ribeiro said Gray addressed his inner circle of advisers before delivering his concession speech late Tuesday. “The mayor’s orders last night were very clear,” he said. “We’re going to provide the best possible service to District residents and visitors.”

The council could be more seriously roiled as Bowser and, to a lesser extent, Catania develop new centers of power over the coming months.

“Now people will expect that Muriel Bowser is the one to call to get something done in government,” said William P. Lightfoot, a former council member is the chairman of Bowser’s campaign. “She is going to be here for the next four years. That puts increased pressure.”

Council Chairman Phil Mendelson (D) said he did not think that either Bowser or Catania should be entitled to special consideration during the budget process.

“Let’s just say she wants to put $100 million into Metro while the mayor wants to put $100 million into affordable housing,” Mendelson said. “I don’t know that the members would just go along just because she is the presumptive mayor. . . . The mayor is still a player in this budget.”

The larger danger in the coming months, Mendelson said, is a brain drain from Gray’s administration as high-ranking executives leave for other jobs. The mayor openly encouraged both contenders for his job to reassure those they intend to keep on — particularly in the education sphere, which he said is “critical not to disrupt.”

“You’ll see people leaving one by one,” he said. “By the end of the year, there could be a half-dozen or more major agencies without directors, and that’s not good for government.”

Also adding to the unrest is the guarantee that at least two and possibly four of the council’s 13 members will be relinquishing their seats come January. Four-term incumbent Jim Graham (D-Ward 1) lost his reelection bid Tuesday, and Tommy Wells (D-Ward 6) gave up his post to pursue an unsuccessful mayoral run.

And the political upheaval could be even further compounded should U.S. Attorney Ronald C. Machen Jr. decide to bring charges against Gray over an alleged role in a secret financing scheme during his 2010 election campaign.

Gray’s loss could affect the timing of any charges. If Gray had won, Machen would have been under public pressure to act quickly to inform voters about what investigators have learned about the mayor in advance of the general election.

Robert S. Bennett, Gray’s attorney, declined to comment Wednesday, but he has previously said he is prepared to go to trial quickly to try to clear the mayor’s name. Gray has not been charged and has adamantly denied wrongdoing. He has said he would remain in office even if he were charged.

But the fact that Gray still holds the title of mayor until January could give him leverage should he choose to engage in plea talks with prosecutors. Just as other District officials have done in recent plea deals, he could use his position as the sitting mayor — for instance, by offering to resign — as a valuable bargaining chip in negotiations.

Former D.C. Council chairman Kwame R. Brown (D) resigned in June 2012 as part of his agreement with Machen’s office to plead guilty to bank fraud. Former council member Harry Thomas Jr. (D-Ward 5) gave up his position in January 2012 after he admitted stealing hundreds of thousands of dollars in city funds.

Gray’s legal situation is not directly parallel to that of other public executives who have been under federal investigation in recent years — in part because of the unusually long nine-month window between the District’s primary and general election.

Detroit’s former mayor Kwame M. Kilpatrick agreed to resign from office when he pleaded guilty to obstruction of justice charges in 2008, years after winning a second term. He was later indicted in 2010 on sweeping federal corruption charges. Former New Orleans mayor C. Ray Nagin was also indicted after leaving office and convicted in February on bribery and fraud charges.

Ann E. Marimow contributed to this report.