Michael Gartner has become the first casualty of the “Dateline: NBC” fiasco, in which the newsmag staged the fiery explosion of a General Motors truck.The embattled NBC News prexy resigned yesterday, leaving day-to-day operations in the hands of his second in command, exec VP Don Browne. In the wake of Gartner’s departure, a short list of candidates has emerged to replace the controversial news chief, including Browne, NBC News Channel prexy Bob Horner, NBC News senior veep Tim Russert and NBC Sports prexy Dick Ebersol. No candidate has emerged as a front-runner. Corridor talk at the Peacock web has even added Tom Brokaw to the list of possible candidates. The “NBC Nightly News” anchor’s contract is up in August, the same time Gartner officially leaves the network. “I’ve got a full-time job already,” Brokaw said. “I certainly have some ideas on how this place could and should be run, but as far as me becoming president of NBC News, I’d say that’s wildly improbable.” At least one other possible candidate, Russert, said he’s not interested in the slot. “I was approached by Bob Wright and asked if I was interested in being considered, but I told him no,” he said. “I like what I’m doing now, between running the Washington Bureau and anchoring ‘Meet the Press.’ “ NBC president-CEO Robert Wright said yesterday that Gartner’s resignation was just the first step in helping to get the “Dateline” issue behind the network. “I’ve got to think everyday it gets better,” Wright said. The executive added that the matter won’t be put to rest until the web receives a final report from an internal investigation and what it does with any recommendations from the report. Wright declined to discuss whatthe potential fallout from the report could be. Many have speculated that the report, which could be issued later this week, will result in the dismissal or suspension of several “Dateline” staffers. In a memo to his staff, Gartner, 54, said he originally wanted to step down in August, when he would have reached his fifth anniversary atop the news division. That anniversary would have given Gartner the distinction of holding the position longer than anyone with the exception of William McAndrew — the division’s first president, who left in 1968. “He is a controversial guy,” Wright said of Gartner. “That’s one of his strengths and his weaknesses.” Wright admitted that Gartner had been a lightning rod for criticism since he joined the Peacock web, and that lately “he certainly became more of a lightning rod then he wanted to be.” According to Wright, the decision to leave was Gartner’s. He was not fired, Wright said, but it became clear to both that Gartner’s other options weren’t any better. Staying would have kept the spotlight on the news division as it tries to deal with the “Dateline” situation. Wright would not offer any timetable for completing the internal study. As for the internal candidates for the position, Browne is seen by some network insiders as too closely tied to Gartner. “I’m a candidate but I have no illusions about my chances — No. 2′s seldom become No. 1′s,” Browne said. “My job now is to get this place back on its feet so there’s a clear understanding of what it stands for and (to) restore morale after we’ve been through a very rough time.” Wright praised Browne as a capable leader. He said having Browne there gives him the luxury of being able to focus on finding the kind of person necessary to lead the news division. He explained that the search would include candidates inside and out of NBC News. Ebersol is a darkhorse because his primary background is in sports. Ebersol also had an unsuccessful foray into news under Gartner overseeing “Today,” which ended with a public mess over the departure of Jane Pauley as co-host. Horner loses some points because he is a relative unknown in the industry. After the news division has taken so much heat, several senior NBC executives think the new president will have to be someone of stature in the industry, and that may mean looking outside the network. “It will have to be someone squeaky clean,” a senior NBC exec said. “Someone like former CBS News president Dick Salant,” who died in late February.