Nigeria's President-elect Shehu Shagari said today his country would continue its aggressive leadership role on southern African policy and supply military equipment to African guerrilla movements "if necessary."

Shagari, 55, said his government will pursue and intensify the militant role Nigeria's military government has followed for the past four years.

A cautious politician, Shagari is expected to take over from Nigeria's 13-year-old military government Oct. 1. He still faces a possible court challenge to his election from one defeated presidential candidate.

The former Nigerian finance minister made his comments at a press conference following a meeting with a U.S. trade mission headed by outgoing United Nations Ambassador Andrew Young. Young also met with Nigeria's present military head of state, Gen. Olusegun Obasanjo, 42.

At independence 19 years ago, Nigeria followed a moderate and Western leaning foreign policy. Today it is firmly in a nonaligned camp and has taken a militant position on white minority governments in southern Africa. Nigeria is black Africa's most populous and wealthiest state, and its voice in foreign affairs has taken on increasing importance in recent years.

Last month, in a step openly designed to pressure the British over southern Africa, the military government nationalized British Petroleum's lucrative oil production holdings here.

The Nigerians had said they took over BP'S operations because the British were taking Nigerian oil to Europe to replace oil London was selling to South Africa from Britain's North Sea oil field. Britain denied the charge.

Young said BP'S former share of Nigeria's present 2.3 million-barrel-a-day production is being sold on the spot market "at a price considerably above the OPEC price." OPEC oil is selling at an average price of $23.50 a barrel. On the spot market, the price is $30.

During a wide-ranging press conference, President-elect Shagari said "I've always been an ardent supporter of" the military government's foreign policy.

"My administration will pursue this (policy) and intensify it," he continued. "There is no justification for discrimination in any country between whites and blacks."

Shagari's reference to discrimination was apparently directed at South Africa's apartheid policy.

"Nigeria will not take kindly toward any discrimination or racism," he said.

Asked if he would give arms to guerrilla movements fighting in Zimbabwe-Rhodesia, Namibia (Southwest Africa) and South Africa, Shagari said "Yes, if necessary, yes."

Nigeria's present coolness toward Britain, however, apparently does not extend to the United States. Young and the U.S. trade delegation were feted and continually applauded during their three-day stay here.

Shagari said he welcomes American investment in Nigeria but added that his country's present willingness to sell oil to the United States is not iron clad. Nigeria is the second largest supplier of oil to the United States after Saudi Arabia.

"No one can say," Shagari said in answer to a question, "what the [future] oil policy will be."

Nigeria was the third country visited, out of seven, of this first major U.S. trade mission to Africa.

In Liberia and in Nigeria, Young raised the issue of a renewed African dialogue with Israel. Both African countries broke diplomatic relations with Israel folloiwng the Egyptian-Israeli war six years ago.

In a private meeting two nights ago, Young brought up the subject with Shagari.

Asked if he were interested in a renewed dialogue with Israel, Shagari said, "If need be, there is no objection."

Young, who sat next to Shagari during the press conference, said he had discussed the subject briefly with the president-elect.

"This is a lot to ask of a government that is forming itself" to take over the administration in two weeks, he said.

Nigeria, which presently sells $5 billion more to the United States than it buys, is expected to earn $15 billion in oil revenue this year. Young said he would have to "try and redress" the imbalance through more U.S. investment and increase trade.

Nigeria has a population of more than 80 million. Businessmen on the trip have characterized the country as a "huge market."

"We do require more investments from the United States," Shagari said, but cautioned that Nigeria would not necessarily be stepping up the import of consumer goods. Shagari said his economic policies would aim at making Nigeria self-sufficient in food and industrial production.

He said he was interested in the "transfer of technology" from the United States.

Present U.S. investment in Nigeria totals $430 million, 75 percent of which is in the oil industry. There are 100 American companies doing business in Nigeria.