JOHANNESBURG, FEB. 19 -- A powerful bomb ripped through a crowded South African-owned bank in the northern Namibian border town of Oshakati today, killing at least 14 persons and injuring 31 more, most of them seriously, police officials said.

Police blamed the blast on the South West Africa People's Organization (SWAPO). It caused the largest loss of life in the 21 years that the guerrilla group has been fighting for independence for Namibia, which is administered by South Africa in defiance of United Nations resolutions.

It came as SWAPO military activity in the border region has fallen off dramatically in the face of heavy South African military pressure on both sides of the frontier.

Police officials in Windhoek said that 10 women, one child and three men, all civilians, were killed. They said all but one woman were black.

A police spokesman, Kirie Durond, said that approximately 55 pounds of plastic explosives were used in the bomb. It completely demolished the branch of the First National Bank in Oshakati, which serves the main South African Army base operating along the Angolan border with Namibia, also known as South West Africa.

Authorities said a fire hampered rescue operations, and that the death toll could rise.

Christopher Ball, chief executive of the First National Bank, flew to Oshakati from Johannesburg immediately after the explosion. The parent bank, South Africa's largest, was Barclays Bank before the British firm divested its holdings in South Africa last year.

Although no group claimed responsibility for the blast, police spokesman Durond said, "This confirms {SWAPO president} Sam Nujoma's New Year's message when he said he will bring the struggle to the home of every Namibian."

SWAPO's spokesman in Windhoek, Hibipo Hamutemya, said his group had nothing to do with the explosion. "The bomb is part of South Africa's dirty propaganda campaign to smear the name of SWAPO," Hamutemya said.

The bank, which was the target of a limpet mine blast last year in which no one was killed, was packed with lunchtime customers when the bomb exploded at 12:55 p.m. today, police said.

The South African Press Association said that most of the customers were employees of the Ovamboland civil administration who had been paid today. The administration governs the 220-mile-wide Ovambo tribal territory and has been criticized by SWAPO as being collaborationist.

Reports from Oshakati said security guards had locked the bank's doors to control the crowd until those inside had been served, and that some customers waiting outside were injured in the blast. The news reports said that some victims inside had been blown apart by the force of the explosion.

The chairman of the Namibian Cabinet, Moses Katjiuongua, said his government was "deeply shocked by the senseless attack on civilian lives and the destruction of property." He said that groups that commit "such brutal deeds are not entitled to enjoy the freedom of the society in South West Africa."

The multiracial transitional government has moved slowly to hammer out a constitution that could lead to independence for the Texas-sized former German colony.

However, negotiations have been hampered by Pretoria's insistence, backed by the United States, that an estimated 40,000 Cuban troops in Angola be withdrawn first.

In 1973, the U.N. General Assembly recognized SWAPO as the "sole and authentic representative of the Namibian people," and five years later the U.N. Security Council passed a resolution calling for South Africa's withdrawal and for U.N.-supervised elections leading to Namibian independence.