JOHANNESBURG, JULY 24 -- South African security police appeared today to move toward a complete shutdown of the country's largest antiapartheid coalition, the United Democratic Front, by arresting its treasurer and at least five officials of its affiliates for questioning, the organization said.

Azhar Cachalia, the front's treasurer and its only senior national official at the operational level not already in detention or forced underground, was released this afternoon after questioning. Such interrogations sometimes are a prelude to detention under the emergency regulations or the permanent Security Act.

Cachalia was taken from his home by police after he issued a statement expressing concern over a police crackdown on the alliance, according to his lawyer and family members. The front includes more than 700 antiapartheid organizations nationwide.

Cachalia's arrest and interrogation followed by two days the arrest of two other senior United Democratic Front officials: Murphy Morobe, the group's publicity secretary, and Mohammed Valli, general secretary. They were detained in Port Elizabeth on Wednesday and are still in jail.

Morobe had been sought by the police since the national state of emergency was declared on June 12, 1986, following months of escalating civil unrest that left more than 2,300 persons dead.

In his statement, Cachalia said 75 percent of the estimated 3,000 South Africans in detention under emergency regulations are affiliated with the front, a figure that he said represents a "systematic and sustained assault at all levels of our membership."

Of the original 19 national executives named in April 1985, the only members not in detention, in exile or underground in South Africa are Cachalia and copresidents Archie Gumede and Albertina Sisulu, wife of imprisoned African National Congress leader Walter Sisulu.

Gumede and Albertina Sisulu, who were acquitted of treason charges 18 months ago, act in a titular and advisory capacity rather than on the operational level. Another copresident, Oscar Mpetha, is in prison in Cape Town.

At the regional level, the western Cape Province branch of the United Democratic Front has been so reduced by arrests that it recently reorganized and appointed new leaders. The top three leaders in the eastern Cape Province are in detention, and half of the Transvaal Province leaders are either in jail or underground.

Ismail Ayoub, Cachalia's law partner, said at least five officials of front affiliates also were rounded up in the police sweep today. Authorities told him that three others were being held for interrogation and that their status would be decided later, he said.

The front was formed in 1983, initially to generate opposition to a national referendum on a tricameral legislature for whites, Indians and mixed-race Coloreds that excluded South Africa's black majority of 23 million. It quickly broadened its base and became the country's most influential antiapartheid group. The government has branded it a cover for the outlawed African National Congress.

Last year, Pretoria declared the front an "affected organization," meaning that it could no longer receive funds from abroad, but the decree was overturned in May by a Supreme Court ruling.