Nigeria, the United States' second-leading oil supplier, announced yesterday that it is raising its petroleum prices $4 a barrel beginning Monday, the stiffest price rise announced by any member of the Organization of Petroleum Exporting Countries this year.

Together with price increases announced by seven of the 13 OPEC members last month, Nigeria's sharp increase will eventually add nearly 7 cents a gallon to demestic gasoline prices, according to industry analysts.

The increases are expected to add about $7.5 billion, or more, to the U.S.

outlay for foreign oil this year.

Nigeria's new price of $34.21 per 42-gallon barrel -- now the second-highest after Libya's at $34.72 a barrel -- is especially significant, because the prized African crude is used almost exclusively to blend gasoline.

The United States imports about 1 million barrels a day from Nigeria, or about 12 percent of the nation's total imports. Saudia Arabia, the nation's leading foreign oil supplier, raised its prices $2 a barrel last Monday, touching off the most recent wave of spiraling petroleum prices.

Britain has been under strong pressure from the State Department and European allies not to raise the price of its North Sea oil, now selling at up to $29.75 a barrel. Yesterday, a senior State Department official said it was not certain whether British would boost their prices, adding, "But so far they have been very helpful."

Ironically, the recent burst of increases comes as prices on Europe's Rotterdam spot market have declined from record levels earlier this month. The spot price drops have been attributed to the continuing high production levels maintained by Saudia Arabia, Kuwait, and Iraq as well as lagging demand for crude oil in the Western industrial nations.

One thing that is certain, according to State Department and oil industry officials, is that this latest round of increases represent a major setback to Saudia Arabia, leader of OPEC's moderate faction, which had hoped to unify the cartel's fractured pricing structure.

Since OPEC's December price-fixing meeting in Caracas, Venezuela, world oil prices have moved up rather than down from the high official prices set by Libya, Algeria and Iran -- the so-called "price hawks."

OPEC's weighted official price has risen from $13.77 a barrel a year ago, to more than $30.00 a barrel.

In a related development French Minister of Industry Andre Giraud said in an interview yesterday that the European Economic Community will open talks "perhaps in the next two months with the Arab Gulf oil producers."

At the State Department, a senior official said there was renewed interest in producer-consumer talks in the Persian Gulf since the Soviet invasion of Afghanistan.

Giraud said the French have discussed talks with the Saudis and Kuwait and are still working on an agenda.

On other issues Giraud said:

France will open a new nuclear power plant every two months from now until 1985, enabling the French to cut their dependence on imported oil from a total of 67 percent of total energy supplies in 1973, to 45 percent by 1986.

The ambitious French nuclear program, Giraud said, results from a fast licensing process limited to 547 days, and wider public acceptance of nuclear power than in the United States.

The U.S. Energy Department's recent sale of Elk Hills reserve oil at $41 a barrel was a "regrettable, even deplorable mistake" because it encouraged a rise in spot-market prices.

Spot prices in France, he said, have been controlled by placing a ceiling price on petroleum products that discourages companies from competing in the high-priced spot market.