Foreign diplomats here have been told that senior Chinese leader Deng Xiaoping, who has not appeared in public for more than six weeks, is avoiding foreign visitors because of an illness, a diplomat said today.

A Foreign Ministry spokesman said, however, that reports of Deng's illness were "a sheer fabrication."

The diplomat said the report about an illness came from Chinese officials, who did not imply that the reported illness was critical. "It could just be a common cold," the diplomat said.

Rumors emanating from Hong Kong that Deng's health had seriously deteriorated surfaced in Peking about two weeks ago.

In response to questions from foreign reporters, a Foreign Ministry spokesman said at the time that the rumors were false and that Deng was in excellent health. Deng, 81, is hard of hearing in one ear, but is not known to be suffering from any major illness.

The Hong Kong stock market index dropped markedly on Jan. 21, and traders said at the time that this might have been partly the result of the rumors.

At a regular press briefing the next day, a Foreign Ministry spokesman repeated that Deng was in excellent health.

Rumors about Deng's health, or even his alleged loss of power, have occurred during previous winters in Peking. This is the time when Deng habitually takes a rest in the south of China. The rumors are fed by his absence.

Despite Deng's efforts to provide for an orderly succession, he cannot guarantee that his sucessors will be able to consolidate their position and continue the economic changes that he and his colleagues have introduced. As some observers see it, Deng still provides the major element of stability.

Deng made his last public appearance on Dec. 14, when he met with former vice president Walter Mondale. A participant said Deng appeared to be in good health then.

Sen. Orrin Hatch (R-Utah) visited here in early January at the head of a five-member congressional delegation that was possibly going to meet with Deng. While the five met with other officials, they did not see Deng.

A delegation from Zimbabwe came to China later in the month, apparently also hoping to see Deng. The Zimbabwe group, headed by Senate President Nolan Makombe, met on Jan. 21 with Chinese President Li Xiannian, but once again, Deng was not available.

In early January, a provincial newspaper, the Liaoning Daily, carried an article stating that Deng had suprised his physicians with the good performance of his heart and lungs. Deng was quoted as saying that this was due to his swimming and bridge playing.

In mid-January, a Peking report said Deng had participated in a bridge tournament on Jan. 12.

On Jan. 24, the official New China News Agency said Deng had issued an order to reward technicians who had contributed to the testing and production of a new type of missile.