In a new escalation of the oil price war, Mexico announced tonight it is slashing export crude prices to $15.07 a barrel, an average reduction of $4.68 -- its second price cut in two weeks.

The price reduction will cut the vital export earnings of Mexico -- a major supplier to the United States -- by an additional $2 billion yearly. The price change is evidence of Mexico's "efforts to remain competitive" in the world oil market, Petroleos Mexicanos, the state oil firm, said in its statement announcing the move.

Buyers here have been anticipating such a move since Venezuela -- another major supplier to the United States -- slashed its "Bachaquero 17" heavy oil by $4.50 to $14.30 a barrel earlier this week.

The price cuts put Mexican oil well below the price of West Texas Intermediate crude, a leading U.S. oil, which sold for about $16.50 a barrel on the open market today. Contract prices posted by U.S. oil companies for the same grade are in the $18-to-$22-a-barrel range.

Mexico's oil price is now nearly $10 below November's $24.50 level, when the government announced its 1986 domestic spending and foreign borrowing plans. Mexico then was expecting to ask for $2.5 billion in fresh credits from commercial banks this year, plus about $1.6 billion from government and multilateral lenders.

For the past five years, Mexico has depended on petroleum revenue for fully two-thirds of its export income. The price reductions are seen as heightening the likelihood of a rescheduling of Mexico's foreign interest payments, expected to total $10 billion this year. Banks also may postpone the collection of a $950 million debt principal payment Mexico is slated to make in April, foreign bankers here said.

The prices announced tonight are retroactive to Feb. 1, and cover the first half of the month, a government spokesman said. Prices for the second half will be set at the end of February, he said.

Because Mexico has been slow to move prices downward, its oil exports so far this year have fallen below an average 1.2 million barrels daily, private industry sources said. In 1985, Mexico exported 1.44 million barrels a day, down from the 1.53 million it had averaged in the three previous years.

"Speaking as a Mexican, not as an oil buyer, I see the price cut as disastrous," said a local representative for a major foreign oil firm. "The news could still get even worse," he added. Mexican energy officials plan to meet with clients and officials from other producing countries Monday at an international petroleum conference in London, industry sources said. The Mexican officials are expected to outline a "more flexible, market-responsive" pricing policy that would be adjusted as often as daily and reflect the current costs of comparable crudes, an analyst at a European oil company said here.

Maya, the heavy crude that accounts for 60 percent of Mexico's export sales, was reduced from $19.50 to $14.60 a barrel for U.S. customers tonight. Mexico's light Isthmus oil was discounted to $16 from $21.70 for U.S. buyers. In Europe and Japan, Mexico's crude prices are slightly lower to compensate for higher transportation costs.

The oil price crunch already is forcing emergency budget cuts within Petroleos Mexicanos, which tonight announced a 30-day postponement of payments to its Mexican suppliers and creditors. "What we were going to pay in March, we will pay in April, and so on," a spokesman for the firm said in a telephone interview. "Everyone will get paid, but there will be a month's delay."

Other large state firms, such as the Federal Electricity Commission, Mexico's national power utility, are also expected to postpone payments to local creditors, according to local press reports this evening. Given the state oil company's position as Mexico's biggest single purchaser of industral raw materials and equipment, a prolonged payments supension could have a devastating impact on much of Mexico's private industry, analysts said.

The payments delay is not expected to affect foreign-based suppliers of the oil firm, but could be applied to Mexican affiliates of international companies, said the Petroleos Mexicanos spokesman, who asked not to be named.