Mexico's state oil monopoly, Pemex, is planning to deliver between 30,000 and 70,000 barrels of crude oil per day to Cuba as part of a triangular oil sales agreement with the Soviet Union.

The agreement was negotiated in Moscow between Soviet officials and Mexican President Jose Lopez Portillo, who visited Moscow last month.

The deal, described by a high Mexican official as "very probable," has not been officially announced yet because "we are waiting for one or two other countries that are involved."

Nevertheless, well-placed sources said the agreement is almost certain to look like this: Mexico signs an export agreement with one or possibly more West European countries that instead of receiving Mexican oil will be supplied by the Soviet Union. Mexico, in turn, will deliver the same amount of crude to Cuba, which now receives its oil all the way from Eastern Europe. Purpose of the deal is to save time and transportation costs.

Most of the Mexico's current export of just over 200,000 barrels of crude oil per day now goes to the United States with a small amount going to Israel. The deal with the Soviet Union is not likely to cut into U.S. purchases of Mexican oil but would come from increasing the amount available for export.

In a separate development, Mexico made a sales contract early last week with the U.S. Department of Defense for the sale of 1.4 million barrels of curde totaling close to $19 million.

This sale, according to Mexican press reports, is destined for the Pentagon's project of building up reserves to safeguard the country against another international oil boycott.