Key Latin American debtor nations will meet late this month to try to find a way to cope with falling prices for oil and other commodities, which are impairing their ability to repay their debts and keep their economies growing.

The emergency meeting was requested by Mexican President Miguel de la Madrid and Venezuelan President Jaime Lusinchi early this month. Foreign ministers of the region decided yesterday to hold the meeting this month in Uruguay. Mexico, the second-biggest debtor in the developing world, will be unable to meet its payments this year on its nearly $100 billion in foreign debts because of the plunge in oil prices. Venezuela, which owes foreigners about $35 billion, has been hard hit by the decline.

In the last month, prices on the spot market for oil -- prices for immediate purchases -- have fallen from about $25 a barrel to about $17. Mexico loses about $550 million a year in revenues for each $1-a-barrel decline in oil prices. It relies on oil for nearly 70 percent of its export revenues and half its domestic taxes.

Latin American ministers have been saying for months that their nations are stretched to the limit in their ability to repay their $360 billion in foreign debts and make a serious attempt to expand their economies. All debtor nations have experienced severe recessions in recent years, and living standards have dropped sharply from their 1981 highs to levels seen 10 years ago.

They believe that a plan to assist the region announced four months ago by U.S. Treasury Secretary James A. Baker III is too modest to make a difference. In a full meeting of the Cartagena group in December, the debtors demanded assistance about twice what Baker proposed. Otherwise, they said, they would be forced to reduce their debt payments unilaterally. The December call for assistance occurred before the plunge in world oil prices.

Uruguayan Foreign Minister Enrique Iglesias, whose tiny nation is expected to host the emergency meeting, said all Latin American debtor nations are being hurt by declining prices of commodities, which make up the bulk of the region's exports. The recent drop in oil prices is the latest manifestation of a problem that has plagued the debt-ridden region for four years, he said.

Commodity prices declined 12.5 percent last year -- after rising in 1984 -- and are 16 percent below 1981 levels. At price levels that prevailed four years ago, Latin American nations would have earned an additional $15 billion to $18 billion from nonoil exports, the minister said in a meeting with reporters here. At that level, countries would have enough funds to pay their debts, invest in their economies and balance their budgets, he said.

Latin American nations owe about two-thirds of their $360 billion in foreign debt to commercial banks, and the rest to other governments or multinational institutions such as the World Bank and International Monetary Fund. An inability of a major debtor such as Mexico or Brazil (which owes more than $100 billion) or of several smaller debtors to pay their debts could throw the international financial system into chaos.

Iglesias said the six nations that make up the steering committee of the Cartagena Consensus -- Argentina, Brazil, Mexico, Venezuela, Colombia and Uruguay -- will attend the emergency meeting. But Iglesias and Mexican Foreign Minister Bernardo Sepulveda Amor said they expect the other five nations in the Cartagena group to attend as well. The members of the steering committee account for about 85 percent of Latin America's foreign debt.

Iglesias said Latin America's current economic needs are so great that additional measures beyond the Baker proposal are needed.

The so-called Baker initiative called for commercial banks to increase their loans to major nations by about $7 billion a year for the next three years and urged multinational institutions such as the World Bank and Inter-American Development Bank to boost their loans by $3 billion a year.

In return, Baker said the developing countries should take steps to remove barriers to economic growth, reduce the size of their state industrial sectors and encourage foreign investment.

The meeting of the top members of the so-called Cartagena Consensus was agreed to yesterday by Latin American foreign ministers who were in town to meet with Secretary of State George P. Shultz to discuss the Central American peace process.

In a communique issued yesterday, the foreign ministers said the decline in oil prices and the continuing low prices for other commodities -- except coffee -- "require urgent mobilization of the mechanisms" created by the full Cartagena meeting in December.

That meeting created the five-member steering committee that is empowered to take action if the region's conditions worsened. Uruguay is a sixth, ex-officio committee member because the country serves as secretariat for the full Cartagena Consensus. The group was named after the Colombian resort where it held its first meeting in June 1984.