Fourteen people were injured today when two terrorist bombs exploded in Windhoek, the capital of Namibia (Southwest Africa) as the South African-governed territory prepared to hold its first elections Monday in defiance of U.N. directives.

Although there have been terrorist attacks in rural Namibia during the long struggle between South African authorities and black nationalists demanding full independence for the territory, it was the first time bombs have been used in the city.

Shortly after the explosions -- one on a busy street and one in a crowded store -- authorities arrested 30 supporters of the Southwest Africa Peoples' Organization on charges that they were advocating violence as they and several hundred others demonstrated against the government.

SWAPO, which is boycotting the election and has threatened to disrupt it, denied any responsibility for today's bombs.

"We had nothing to do with it," Mokganedi Tlhabanello, SWAPO's information secretary, told the South African Press Agency.

Nonetheless, many people, especially the 100,000 whites living in Namibia, are sure to see the bombings as the work of SWAPO. The bombings and the demonstration that followed could signal that the coming five-day election period will be accompanied by more violence and activist opposition than was expected.

These feelings will be reinforced by a statement in Windhoek by South African Police Commissioner Victor Verster who said the police had determined that the explosives used in the blasts were "of Russian origin" and were similar to those "used by SWAPO terrorists" in two bombings earlier this year on rural transport lines.

Verster said he expected there would be more bombings "in compliance with threats issued by several SWAPO leaders here and abroad."

SWAPO is waging a bush war against South African troops in Namibia and opposes the elections because they are not under United Nations supervision.

The explosions occurred only hours after Foreign Minister Pik Botha arrived back in South Africa from a fiveday visit to the United States during which he talked with President Carter and U.N. Secretary General Kurt Waldheim.

Those talks failed to persuade South Africa to call off next week's elections or at least to make an unequivocal commitment to allow U.N. supervised elections in the territory sometime next year.

South Africa has said only that it will "use its best efforts" to persuade the winners of next week's elections to agree to U.N. organized elections so the territory will have an internationally recognized independence.

The United States, France, Britain, West Germany and Canada have said they will ignore the coming election, regarding it as "null and void."

The five Western powers, who drew up the U.N. plan for internationally supervised elections, fear that once leaders are elected under the South African-sponsored voting, South Africa will gradually allow them to assume administrative powers and then unilaterally will give them independence after having frozen out SWAPO and other black nationalists. This independence would probably not be recognized by the international community.

The five Western allies also fear that refusal of South Africa to go along with U.N. elections next year will mean an increased guerrilla war. Cubans and East Germans are reportedly assisting the Soviet-armed nationalist movement at bases in southern Angola.

South Africa has administered this mineral-rich and sparsely populated country since 1920 when it was given a mandate over the former German colony by the old League of Nations. This mandate was revoked by the United Nations and over the past three decades, Pretoria has come under fire from the world community for applying its racially discriminatory political and economic systems to the territory.