MEXICO CITY, AUG. 14 -- Mexico, flush with new bank loans, unexpected oil revenue and greater export sales, has built its international reserves up to at least $15 billion, analysts say.

Just a year ago, the country was running low on cash after international oil prices tumbled, slashing the crude earnings of the oil-dependent nation.

As a result, the government was forced to negotiate a $14.4 billion rescue package with international financial organizations, foreign banks and industrialized nations.

Government officials have been slow to spend the money, concerned in part about the effect of a huge injection of cash into the economy, already suffering from high inflation. Treasury Secretary Gustavo Petricioli told local reporters this week, "We cannot nor should we squander or waste these reserves."

The government, he said, needs a cushion of money in case of changes in the international economy.

Moreover, he said, President Miguel de la Madrid's administration wants to leave enough money in the coffers to give the next president room to maneuver in developing an economic plan. De la Madrid's term expires at the end of 1988. His ruling Institutional Revolutionary Party is scheduled to announce shortly its presidential candidate.

"They are having a difficult time figuring out how to use the money without causing an inflationary impact on the economy," said a financial analyst who spoke on condition of anonymity.

Consumer prices skyrocketed 67.5 percent in the first seven months of this year, and analysts predict a pace of 120 percent or more for the year as a whole. The inflation rate reached a record 105.7 percent in 1986.

The analyst who requested anonymity said the government is considering ways of using the money to reduce its huge foreign debt of about $105 billion, the second highest in the developing world after Brazil.

Under one option, the government would buy back some of its loans from foreign banks at a discounted rate, which would ease the country's burden of interest costs on the debt. The government is expected to pay about $8 billion this year in interest charges.

On Friday, Mexico signed an agreement to reschedule $9 billion worth of Mexican private sector debt. The pact was reached with 210 international banks.

The increase in the reserves is attributed to a variety of factors:

The nation has had a fresh injection of foreign loans. On April 30, the government drew $3.5 billion of the $7.7 billion commercial loan package. Companies have increased their exports. The government reported a trade surplus of $4.5 billion in the first six months of 1987, up 203 percent from the same period a year ago. Oil prices have risen to around $20 a barrel on the world spot market. Petroleum exports grew 38.1 percent in the first six months of the year. Mexicans who socked away millions of dollars outside the country at the start of the economic crisis have brought some of the money back to invest in their companies, the booming stock market or other high-paying instruments