China's Communist Party chief, Hu Yaobang, has warned that the United States could be violating a major agreement with China by supplying military technology to the rival government of Taiwan for its development of an advanced jet fighter plane.

In an interview yesterday with Selig S. Harrison, senior associate of the Carnegie Endowment for International Peace, Hu said China is "not satisfied" with U.S. observance of the 1982 Sino-U.S. agreement on U.S. arms sales to Taiwan.

Hu, who is expected to succeed Deng Xiaoping as China's senior leader when Deng retires, warned that "if the U.S. remains unfriendly over a long period of time, we will not tolerate that."

This was the first time that a Chinese leader has publicly raised objections to reports that the United States is licensing U.S. companies to provide technology and some components for the projected Taiwan fighter. His remarks raise the possibility of reopening the most contentious issue in Sino-U.S. relations: U.S. arms sales to Taiwan.

Harrison, a former Washington Post reporter in Asia, made the interview with Hu available to The Post. The interview -- which included the topic of Taiwan at Harrison's request -- lasted nearly two hours, half of it devoted to Taiwan. More than a dozen Chinese officials and foreign affairs specialists, including Zhu Qizhen, China's veteran vice minister of foreign affairs, also attended the meeting.

While Hu spoke strongly against technology transfers to Taiwan, he sounded more flexible when it came to China's longstanding offer of autonomy for Taiwan. For the first time, he described the Nationalist government on Taiwan as a "legal" government.

Diplomats here said they considered this an "interesting" overture and an attempt on Hu's part to demonstrate more flexibility toward Taiwan, which the mainland regards as a breakaway province of China.

Taken together, Hu's remarks were the most extensive comments in some time by a Chinese leader on the sensitive issue of Taiwan.

The General Dynamics Corp. is "a design consultant" to Taiwan on development of the new plane, according to sources, and U.S. defense publications have reported that engine development is being conducted under a joint venture between the Garrett Corp. and Taiwan's Aero Industry Development Center. The current issue of Aviation Week reports that the range and payload of the new engine will be similar to those of the Northrop F5E now used by Taiwan's air force.

Some specialists estimate it will cost Taiwan more than $1 billion to build the plane.

U.S. Embassy officials and spokesmen for General Dynamics and Garrett declined to comment on the reports. But a spokesman for Taiwan's office in Washington, the Coordination Council for North American Affairs, said, "We stand by the [Aviation Week] article."

Following the Reagan administration's decision this year to sell China $550 million in aviation electronics to upgrade Peking's most advanced interceptor aircraft, Taiwan and its backers in the U.S. government have begun pressing the administration to upgrade the F5E fighters, contending that improved Chinese F8s would erode Taiwan's traditional air superiority.

Hu challenged Washington's view that U.S. government-licensed transfers of technology to Taiwan are permitted under the 1982 Sino-U.S. agreement, which provides for a "gradual" reduction of arms sales to Taipei.

"The transfer of technology sounds better, but arms sales and the transfer of technology for arms manufacture are the same thing," said Hu.

Hu told Harrison that "there appear to have been a whirlwind of secret dealings" between Washington and Taipei concerning Taiwan's plans to build the fighter.

A senior Taiwan official said last November that Taiwan hoped to build a plane superior to the F5E fighter. The United States, in order to avoid provoking Peking, has refused requests by Taiwan and its U.S. backers that Taipei be allowed to purchase the more advanced F16 or F20 jet.

The Chinese fear that if the United States does not cut off arms sales and technology transfers to Taipei, Taiwan will develop an independent capability to produce an extensive range of weapons and then indefinitely resist Peking's negotiating offers.

Arguing that Peking still wants to take over Taiwan, Taipei so far has resisted such offers.

In the interview, Hu referred to the ruling Kuomintang government on Taiwan led by President Chiang Ching-kuo as "a government established in a legal way by elections." Although he did not specify in the interview, China has always avoided characterizing Taiwan as a sovereign government and it appeared that Hu was still referring to a government is somehow a subsidiary part of China.

Asked by Harrison if it enjoyed popular support, Hu said that "support is another question, but it is a legally established government," and he renewed offers to negotiate with Chiang.