China's two top security officers during the Cultural Revolution, secret police chief Kang Sheng and public security minister Xie Fuzhi, have been expelled posthumously from the Communist Party, the New China News Agency reported.

The expulsions came on the eve of the trial of the Gang of Four radical leaders headed by Mao Tse-Tung's widow, Jiang Qing, and six other defendants accused of plotting against the party and state.

Xie, who died in 1972 at the age of 75, and Kang, who died three years later at the age of 69, rose to power during the Cultural Revolution in the mid-1960s.

Kang Sheng became "adviser" to the Cultural Revolution group that led China into 10 chaotic years and resulted in attacks on head of state Liu Shaoqi and Deng Xiaoping, now the driving force behind China's modernization.

The news agency quoted the announcement by the party central committee as saying that "Kang Sheng and Xie Fuzhi . . . directly participated in scheming by [the late defense minister] Lin Biao, Jiang Qing and company to usurp the supreme leadership of the party and state during the 'Cultural Revolution' and committed grave crimes."

Meanwhile, police rounded up at least 15 young demonstrators marching on the Chinese government complex and took them away in a bus, witnesses said. It could not be determined what the petitioners were protesting.