Chinese and U.N. officials have signed an agreement to give Peking $20 million to aid 251,000 Vietnamese refugees, the largest number accepted by any country, U.N. officials said.

Alexander Casella, chief of the East Asian regional section of the U.N. High Commissioner for Refugees, said the money would also cover costs of chartering Chinese aircraft to take 10,000 refugees from camps in Thailand, Malaysia and Hong Kong to new homes on China's Hainan Island.

Most of the refugees are ethnic Chinese who have come from North Vietnam to severely strained facilities in the four southern provinces where they have been settled. Peking in the past declined to accept international relief aid but has changed its policy under the pressure of the rufugee flow and because of a general softening of its earlier, stern self-reliance policy.

Casella said $5.5 million will provide housing, medicine and fishing equipment for 11,000 refugee fishing families, $4.4 million will help 39,000 farmers who still lack permanent settlements, $2.7 million will help house 100,000 who still lack proper shelter, $3 million will help build the new Hainan Island settlements and the remaining money will pay for transportation and emergency food rations. a

Casella said Peking will be spending about four times the U.N. contribution on each project. The aid is to last until the end of 1980, with a permanent U.N. refugee aid representative, Jacques Mouchet, living in Peking to oversee the program. The 10,000 new refugees to be brought to China are mostly Laotians who have no hope of settlement in the West, officials said.

News services also reported these developments:

A seven-member U.S. congressional women's delegation toured Indochinese refugee camps Sunday in eastern Thailand, Reuter reported from Bangkok.

The group then left for Phno mPenh to try to persuade the Vietnam-backed government to allow more aid for Cambodia.

The Soviet Communist Party newspaper Pravda charged that First Lady Rosalynn Carter's journey to Cambodian refugee camps in Thailand was part of a U.S. plan to subvert the pro-Moscow Cambodian government of Heng Samrin, the Associated Press reported from Moscow.

The pravda commentary said that by sending his wife to Southeast Asia, President Carter "managed to chuck a stone at the government of Kampuchea [cambodia] by saying that it is preventing aid from reaching starving people."