BEIJING — Barely two months into their jobs, the Communist Party’s new leaders are being confronted by the challenges posed by a constituency that has generally been one of the party’s most ardent supporters: the middle-class and well-off Chinese who have benefited from a three-decade economic boom.

A widening discontent was evident this month in the anticensorship street protests in the southern city of Guangzhou and in the online outrage that exploded over an extraordinary surge in air pollution in the north. Anger has also reached a boil over fears concerning hazardous tap water and over a factory spill of 39 tons of a toxic chemical in Shanxi Province that has led to panic in nearby cities.

For years, many China observers have asserted that the party’s authoritarian system endures because ordinary Chinese buy into a grand bargain: the party guarantees economic growth, and in exchange the people do not question the way the party rules. Now, many whose lives improved under the boom are reneging on their end of the deal, and in ways more vocal than ever before. Their ranks include billionaires and students, movie stars and homemakers.

Few are advocating an overthrow of the party. Many just want the system to provide a more secure life. But in doing so, they are demanding something that challenges the very nature of the party-controlled state: transparency.