IN NO JURISDICTION will the Reagan budget cuts be felt more sharply than in the Commonwealth of Puerto Rico, where federal assistance now accounts for over one-third of the government's normal revenues. Puerto Rico will take its share of reductions in the whole range of domestic programs -- health, education, jobs, housing and so forth. It will also be called upon to absorb an especially harsh immediate 25 percent cut in food assistance -- and apparently more in future years as food prices increase -- as the result of provisions in the budget reconciliation bills replacing the food stamp entitlement program with a block grant of fixed amount.

Food stamps have always been a mixed blessing for the Puerto Rican economy. As the source of almost 10 percent of the island's personal income, the stamps have certainly bolstered the purchasing power of its many poor citizens, but they have also become a symbol of Puerto Rican dependence on mainland largess. Almost 60 percent of the population now participates in the program, and the stamps are said to circulate widely as a black market currency for transactions far removed from the program's nutritional goals. The sudden surge of food demand after the program was introduced in 1975 drove up food prices, shifted food consumption patterns toward the high-priced products of the mainland and may have hastened the disastrous decline of Puerto Rico's agriculture. In a low-wage, high-unemployment economy, food stamps worth as much as $2,650 a year to a family of four, and much more to Puerto Rico's typically large family, may also seem an attractive alternative to full-time work.

It came as no surprise that guaranteeing U.S. nutritional standards in a country where per capita income is less than half that of Mississippi would flood the island with stamps. Fear of similar inundations had led earlier Congresses to put artificial ceilings on Puerto Rico's share in such other programs as welfare, Medicaid and revenue sharing with the result that federal aid to Puerto Rico is now about $700 million less than it would otherwise be. In the case of the food stamp program, however, with its explicit goal of ensuring a nutritionally adequate diet, an arbitrary cap on benefits was harder to justify -- especially since other welfare aid was so limited.

Deciding what is fair and sensible in the dealings between a wealthy nation and its poor dependents is obviously beyond the demonstrably crude techniques of the budget reconciliation process. Perhaps, in the long run, Puerto Rico will be better off with fewer stamps and more flexibility to tailor the program to its own needs and economic conditions. But there is something unacceptable about a prosperous country, about to treat itself to a triple round of tax cuts, suddenly deciding to lop 25 percent from the food budgets of two million voteless American citizens living well below the poverty line.