BEIJING — With still no sign of China’s designated new leader, Xi Jinping, who has not been seen in public since Sept. 1, many insiders and well-connected analysts say the Chinese political ship is adrift, with factions jockeying to shape an impending Communist Party conclave.


The government has maintained its official silence about Mr. Xi’s absence. After an initial burst of chatter, blog posts alluding to Mr. Xi have been effectively smothered on China’s social media platforms, and China’s beleaguered Foreign Ministry spokesman says on a daily basis that he has no information, despite a barrage of questions from the foreign news media.


By Thursday, a number of ranking party members with years of experience following Chinese politics were generally in agreement that Mr. Xi, 59, had suffered either a mild heart attack or a stroke, forcing him to cancel his appointments.


“The most reliable information we can find is that it’s his heart,” said a senior Chinese newspaper editor who spoke only on the condition of anonymity because of the sensitivity of the issue among the party hierarchy. Li Weidong, a former editor of a government-sponsored reformist journal, agreed.


On Thursday, Mr. Xi’s name appeared in the Chinese press for the first time in days, as he offered condolences over the recent death of a veteran party member. But that terse report only mentioned him among several leaders and did not imply anything more than a formal expression of sorrow.


“I think it’s hard to say this proves anything,” said Jin Zhong, the editor of Open, a magazine in Hong Kong. “He didn’t appear, but just sent condolences.”


Even if Mr. Xi does soon show up in public, he will be re-entering an unexpectedly contentious political arena.


Planned years in advance, the 18th Party Congress is slated to be the most sweeping government reorganization in a decade, with scores of leaders scheduled to retire. It was still expected to take place next month or soon after in Beijing, where Mr. Xi was to take over as leader from Hu Jintao. The Communist Party has numerous factions, but the overall framework of the transfer was thought to have been mostly ironed out over the past year.


But recent developments, including Mr. Xi’s mysterious cancellation of several public appearances, suggest that may not be the case.


The most obvious sign of discord is that the dates for the congress have not been set. Most political experts here expected it to be held in mid-October, but without an official announcement, some are predicting it will be delayed.


“We hear that the congress will be held in late October or early November,” a security official from southern China said. “Currently we’re planning for that.”


One reason for the delay, the experts say, is what now appears to have been a contentious meeting in early August at the seaside resort of Beidaihe, China. According to the official script, this was to have been the final big meeting before the congress of leaders from the party’s various factions: the military, big state enterprises, descendants of revolutionary families, leaders of critical Communist Party organizations and others. The details of the congress were to be finalized at Beidaihe and the dates announced later in August.


Instead, according to information that is slowly leaking out, the Beidaihe meeting and other sessions beforehand in Beijing were especially tense. “The atmosphere was very bad, and the struggles were very intense,” said a political analyst with connections to the party’s nerve center, the General Office.


Mr. Hu, who has been criticized as having been an overly cautious and ineffective leader during his decade in power, was also seen as defensive and gloomy.


A veteran party scholar who attended the Beidaihe meetings said the leaders only met over a couple of days and finalized a list of more than 2,000 delegates to the congress whose names were already public. A proposed list of new leaders was not circulated, however, and there was no deliberation of critical issues, like drafts of the political blueprints to be unveiled at the congress, he said.


“We thought that these issues would be settled there,” he said, “but they weren’t.”


Given the absence of hard information from the government, it is possible that Mr. Xi’s absence has been caused by something other than illness. The veteran party scholar, who dined late last week with a close family member of Mr. Xi’s, said the relative told him he did not know Mr. Xi to be sick. The scholar maintained that Mr. Xi’s absence was more likely because of the unsettled political situation.


“There is still a struggle; it is not finished,” he said.