Former president Carter, ending a 10-day visit to China, said today he expects continued growth in Sino-American relations in the Reagan administration but warned that the Taiwan issue poses a serious problem.

Carter said he was "surprised and impressed" by the vehemence with which all the senior Chi-nese leaders spoke to him of the Taiwan problem, "not as a threat but as a firm statement that this issue is of profound importance."

China, which consistently opposed U.S. arms sales to Taiwan, has been increasingly vocal on the issue since the Reagan administration came to power, expressing special anxiety about the sale of sophisticated warplanes or other high-profile military items to the island bastion which it considers a wayward province.

Carter, who announced nearly three years ago that arms sales to Taiwan would continue even as he was normalizing Sino-American relations, seemed today to suggest more qualifications and limitations on those sales than ever before.

On arrival in Osaka, Japan, from Shanghai today, Carter, who rejected the neutron weapon, said he did "not disagree" with the President Reagan's decision to manufacture it, Associated Press reported.

Carter said Soviet intervention in Afghanistan and "encouragement of Vietnam's invasion of Kampuchea (Cambodia)" had turned his commitment to arms reduction into a "fruitless search," AP reported.

Meeting reporters over breakfast before departing for Japan, Carter said his policy--"clearly described" to the Chinese at the time of normalization--was that U.S. weapons for Taiwan would be "defensive in nature," "not advanced" and "no threat to the mainland."

The hour-long session at his Shanghai hotel was the former president's most extensive press conference since leaving the Oval Office Jan. 20. It was almost entirely devoted to summing up impressions and views about China arising from his current journey.

Following the normalization of Sino-American diplomatic relations in January 1979, Chinese Vice Premier Deng Xiaoping visited Washington and toured the United States. The original plan had been for Carter to return the visit early in 1980 and for Chinese Communist Party chief Hua Guofeng to visit Washington and other U.S. points early this year. The taking of the U.S. hostages in Iran caused Carter to postpone his trip to China. Now both he and Hua are out of power.

In three days in Peking last week, Carter saw all three top Chinese leaders, Deng, Premier Zhao Ziyang and the new Communist Party chairman, Hu Yaobang. Carter is the first senior American to meet Hu, whom he described today as "dynamic...friendly...eloquent" and seemingly very strong politically.

After Peking, the former president toured the ancient and archaeologically important city of Xi'an, the gardens of the city of Suzhou, and Shanghai, China's largest and probably most westernized city.

In addition to sightseeing and partaking of elaborate banquets, Carter visited a computer laboratory, a rural commune, submarine and surface ships of the fleet, a shipyard, factories producing silk rugs, embroidery and furniture, a technical university, a Protestant church and an urban residential complex.

It was in the department store of the Shanghai residential complex on Wednesday that a 51-year-old man was seized by Chinese security as he broke through police lines and grabbed Carter's left arm, evidently in an attempt to hand him a letter expressing a personal grievance.

Chinese officials said the unnamed man is mentally unstable. Carter, quoting an official report, said the letter complained of "inadequate health care." According to authorities, the petitioner meant Carter no harm and has been released from police custody after questioning.

Beyond his formal program, the ex-president mixed with the people to an unusual degree in a series of early-morning bicycle rides, walks and jogs. He went to marketplaces, was invited impromptu to Chinese homes, and chatted informally with dozens of Chinese at random.

Carter praised the authorities for their "lack of restraint" on his movement, especially his 5:30 a.m. travels. He also praised the people's spontaneous warmth, which he said "could not be contrived."

Carter appeared on a 30-minute nationwide television interview, a rare opportunity for a foreign guest.

The former president disclosed that he had spoken to senior Chinese officials about the human rights of two political dissidents whose cases were brought to his attention by Amnesty International. He also revealed that he had taken up with the leaders the living conditions of American exchange students, pleading that they not be segregated from their Chinese counterparts.

Asked what he anticipates for China's future, the ex-president said that, despite "obvious economic difficulties" inherent in a nation of a billion people, he believes "China's influence in the world will be steadily increasing--economic, political, military, cultural."

Carter called for a "coalition" or "arrangement" involving the United States, China, Japan, Western European nations and noncommunist Asia to oppose "aggression" in Afghanistan and Cambodia and "prevent this occurring in the future."