The difficulty that seems to plague America's interventions in foreign countries is highlighted in the latest news from and about El Salvador. The so-called ''death squads,'' right-wing killer groups that frustrate such reform efforts as land redistribution, are active again. They are so active - and so much out in the open - that Washington has been forced to protest and condemn them.
The latest round began on Sept. 20 with the kidnapping of Amilcar Martinez Arguera, director of Economic and Social Affairs in the Salvadorean Foreign Ministry.
The US Embassy on Sept. 23 condemned the kidnapping and called for the release of Mr. Martinez.
The embassy's statement said:
''We urge those responsible to desist from a path which is doing more to destroy El Salvador than the Communist guerrillas could ever hope to accomplish.''
An organization calling itself the Maximilian Hernandez Anti-Communist Brigade asserted that it had done the kidnapping.
Another group, calling itself the Salvadorean Nationalist Command, issued a statement criticizing the US Embassy for criticizing the kidnapping.
A third group, called the Secret Anti-Communist Army, has joined in the new practice of issuing public statements. Its latest criticized the provisional government of El Salvador for attempting to negotiate with the insurgents, which the United States is pressing the Salvadorean government to do.
The kidnapping of Mr. Martinez followed a rise in the frequency of killings, bombings, and kidnappings for which the right-wing groups claim credit.
On Oct. 3 the State Department backed up the embassy in San Salvador, saying:
''We have consistently deplored political violence regardless of its origin and, in the context of reports over the past few weeks, do so again in the most categoric terms. We support the US Embassy's statement last week against this violence.''
The Reagan administration in Washington is required by Congress to report every six months on ''progress'' in El Salvador toward respect for human rights and life. US military aid to El Salvador is authorized by Congress on the condition of such ''progress.''
The latest affirmation of ''progress'' was made on July 20. Aid now consists of weapons plus training of Salvador Army units in Honduras plus US military advisers inside El Salvador.
The provisional government of El Salvador is dedicated officially to reform, including land redistribution. The land-reform program had a promising beginning. It is now virtually dormant, partly because of civil war, partly because of government inertia under right-wing resistance, and partly due to the work of the ''death squads.''
Whispered threats are often enough to discourage villagers from taking up farm plots. Those who do take up plots sometimes ''disappear.'' It has become ''unhealthy'' to apply for land under the redistribution program.
US aid to the government of El Salvador is prompted by the best of motives. The purpose is to protect the people from the tyranny of a communist dictatorship. But the net effect is tending to be the perpetuation of a propertied oligarchy backed by the ''death squads.''
The US intervened over a longer time and more directly in Nicaragua than in any one other Latin country. The end result was the Somoza regime, so brutal and undemocratic that everyone but its own members agreed that it had to go. At the end, even Washington concurred in its overthrow.
If US intervention could bring real democracy and reform to a Latin country, everyone west of the Iron Curtain would cheer. But nearly three years of Reagan intervention in El Salvador provides little hope of such an outcome there. Based on the record to date, the prospect is that the old oligarchy, backed by its ''death squads,'' will win out and run the country - until another revolution comes along.