Only 12 of the accused were named. Ten reside in the United States and two in China. Mr. Hickton said he hoped that Chinese officials would cooperate with his office.

Suspicions about international students cheating on American university entrance exams have swirled in recent years. Last fall, for example, test scores of thousands of students from China and South Korea were temporarily withheld while test officials looked into suspicions of cheating. The Educational Testing Service, which administers the SAT, reviewed the scores and decided not to release some of them to colleges because of concerns about their validity.

According to the Institute of International Education, China sends more students to study in the United States than does any other country; 31 percent of the international students in the United States during the 2013-14 academic year came from China. That year, 274,439 Chinese students studied in the United States, an increase of 16.5 percent over the previous year.

The indictment says the conspiracy went on for four years, from 2011 to earlier this year. It says the beneficiaries of the scheme used online messaging services to request that an impostor take an exam in their name. The beneficiaries then provided the test takers with a copy of their passport. A false Chinese passport was then produced, bearing the test taker’s face and the beneficiary’s identifying information, which the test takers used to identify themselves and sit for the exam.

For example, in February 2012, a passport bearing the name of Siyuan Zhao but showing the face of a different person, who was redacted in the indictment, was mailed to Western Pennsylvania. That March, an unnamed person pretended to be Mr. Zhao and took the Toefl exam and, later that month, Mr. Zhao had the results of that exam forwarded to Northeastern.