U.S. Defense Secretary Harold Brown said tonight that the United States and China could respond with "complementary" military action if jointly threatened. Aides said it was his strongest statement yet on countering Soviet aggression with Chinese help.

At a welcoming banquet given by Chinese Defense Minister Xu Xiangqian, Brown said he wanted to "exchange views" on how the United States and China "might facilitate wider cooperation on security matters." Such cooperation, he said, "should remind others that if they threaten the shared interests of the United States and China, we can respond with complementary actions in the field of defense as well as diplomacy."

In a briefing following the banquet and Brown's lengthy toast, U.S. official acknowledged that the U.S. policy of evenhandedness in dealing with the Chinese and the Soviets had become "frayed" as a result of recent Soviet behavior, particularly in the invasion of Afghanistan.

The official reaffirmed that there were no plans for U.S. arms sales to China, but refused to say what other specific measures would be discussed during Brown's week-long visit. He indicated, however, that there would be announcements of some sales of U.S. technology of possible military use to China.

The Chinese underlined their deep interest in cooperation to frustrate the Soviets by publicizing a statement by influential Vice Premier Deng Xiaoping at a banquet honoring Egyptian Vice President Mohammed Hosni Mobarak here tonight. Deng called the invasion of Afghanistan "a grave step taken by the Soviet Union to make a southward thrust to the Indian Ocean, control sea lanes, seize oil-rich areas and outflank Europe so as to gain world hegemony."

Deng repeated Peking's "firm demand" that Soviet troops be withdrawn, and he said the Chinese would "work together with the Afghan people, and all countries and people who love peace and uphold justice, to frustrate Soviet acts of aggression and expansion."

Deng is scheduled to meet with Brown Tuesday. A U.S. official emphasized Deng's influence over Chinese foreign policy, and said he expected a clear view of the Chinese reaction to Brown would emerge only after that Tuesday meeting. The official said it was difficult to predict what would come out of Brown's visit, since no agreements had been prepared in advance and the Afghanistan situation had suddenly increased the significance of the meeting.

In his toast welcoming Brown, who is the first U.S. defense secretary to visit China, Defense Minister Xu also referred to Moscow's "massive armed invation" and "military occupation" of Afghanistan. He told Brown and the assembled Chinese and American military leaders and diplomats that "all the justice-upholding countries and people should get united, take effective measures and fight relentlessly in defense of world peace against hegmonism."

Brown mentioned in his toast the American hostages still held in Iran, the Soviet-backed Vietnamese invasion of Cambodia and the "effort to subjugate the Moslem people of Afghanistan." He said, "Under these circumstances, increased cooperation between China and the U.S. can be an important -- and is a needed -- element in the maintenance of global tranquility."

Brown said that during his visit here, "It is particularly important that we discuss the situation in Afghanistan, Pakistan, Iran, Indochina, and northeast Asia." He said his delegation would explore with the Chinese the question of arms control and "arrangements for expanding" contacts between "our defense establishments."

Xu and Brown dined in the Jiangsi Room, a small banquet hall in the Great Hall of the People. They kept the other guests wiating an unusually long time before dinner while they chatted behind closed doors. One official said their conversation was mostly of shared concern about Soviet aggression.

In his background briefing, the U.S. official hinted that the United States expected that both China and the United States would cooperate in efforts to supply military equipment to Pakistan, threatened by the fighting in Afghanistan.

Brown said cooperation with Peking "offers mutual benefits" and "endangers no third party" but the attacks on the Soviet Union in the rest of his speech rivaled the rhetoric of the official Chinese press in sarcasm and venom toward Moscow.

"The Soviet Union has overthrown a friendly government -- one with which it had a peace-and-friendship treaty," Brown said of the Afghan situation. "It has expressed its friendship by having the president of that government and his family executed."