Ratification of the treaty would “promote and realize the principles of a country based on human rights and a China governed by its Constitution,” the petition said. “We fear that due to the lack of nurturing of human rights and absence of fundamental reverence and assurances for individuals’ freedom, rights and dignity, if a full-scale crisis breaks out, the whole society will collapse into hatred and brutality.”

The call, also circulated by e-mail, carried the names of 121 backers, including several who said they lived in Hong Kong or Macau.

The petition was the latest display of the demands for political change confronting China’s new leadership. Several people who signed it said they hoped to press Mr. Xi and his colleagues to live up to vows of greater respect for the rule of law and citizens’ rights that Mr. Xi and other officials have made since he became Communist Party leader in November, when Mr. Hu retired from that post.

“This has become increasingly important because on the one hand violations of rights have become so common, while on the other hand citizens’ awareness of their rights has risen sharply,” said Cui Weiping, a translator and essayist in Beijing who signed the petition. “This proposal is really quite mild,” said Ms. Cui, who formerly taught at the Beijing Film Academy. “I see this as giving the government a chance to show that it is willing to make improvements.”

Since Mr. Xi came to power, Chinese advocates of political liberalization have urged the Communist Party to abide by the Constitution, which in theory offers some protection of free speech and other rights. Some reform advocates see some signs of hope in the government’s vow to overhaul “re-education through labor,” which is used to jail citizens without trials, and some point to Mr. Xi’s own promises of greater official accountability.