In one of its sharpest attacks on President Reagan since he took office, China today accused the American leader of having "seized away" Chinese tennis star Hu Na from her parents by personally deciding to grant her political asylum in the United States.

People's Daily, the Communist Party newspaper, also branded as "stupid" U.S. policy makers' handling of relations with China.

The prominently displayed commentary in the newspaper's Sunday edition said, "The president of an awe-inspiring big power . . . has seized away alive a Chinese girl from her own parents and has offered himself as her foreign father."

The editorial was one of the most stinging in a fusillade of anti-American rhetoric touched off here last week by a Reagan administration decision Monday to approve the 19-year-old tennis star's request for asylum. Peking Thursday responded by severing all sports and official cultural exchanges with the United States this year.

Western diplomats here speculated that the sharp personal attack on Reagan today reflected a widely held belief among the Chinese leadership that Reagan had deliberately snubbed the country's top leader Deng Xiaoping by brushing aside Deng's personal appeal to return Hu to China.

Deng is believed to have pressed the issue with Secretary of State George P. Shultz during talks in Peking in February. China repeatedly has issued public guarantees that Hu would not face political persecution if she returned home. The Chinese press has given prominent play to the anguished pleas of Hu's family and former teammates calling on American leaders to "release" her.

The Reagan administration's action on the issue, diplomats here said, represented a major loss of face for Deng in a politcal culture where such considerations are paramount. Deng reportedly has been under fire from hard-line opponents who charge that his reformist policies and pursuit of relations with the United States have compromised China's sovereignty and "national dignity."

Hu, China's top-seeded woman tennis player, left her team while competing in an international tournament in Santa Clara, Calif., last July. She requested asylum in the United States on grounds that she faced persecution in China for her refusal to join the Communist Party and serve as one of its socialist models for youth.

During the nine months leading up to the asylum decision, American officials here repeatedly countered heated Chinese protests by pointing out that under the U.S. system of justice they "could not simply put her on a plane and send her back to China" even if her request was not granted, diplomatic sources here said.

The People's Daily commentary today rejected what it called "the farce of so-called legal procedures," accusing Reagan of personally instigating Hu Na's defection.

It cited April 7 dispatches from American news services quoting Republican fund raiser Richard A. Viguerie as saying that Reagan "has decided to pay any price" to allow Hu Na to stay in the United States. The commentary quoted Viguerie as saying that Reagan had told him, "I will personally adopt her before I send her back."

The official Communist Party newspaper also quoted a report in The Washington Post as saying the final decision was made by "government higher-ups." The Washington Post news story April 5 said: "The final decision on the case is said to have been taken at high levels of the administration."

"Now, who after all made such a decision?" People's Daily asked, concluding: "President Reagan himself gave the answer."

The paper quoted Reagan as saying earlier this year, "It would be stupid if we don't strive to maintain good relations with the People's Republic of China."

"We only wish," it said, "the U.S. government policy makers would not be so stupid."