The turbulence in Central America: Is the US repeating old mistakes?; Violent Neighbors, by Tom Buckley. New York: Times Books. 343 pp. $17.95.

''Violent Neighbors'' is American journalist Tom Buckley's assessment of the turbulent atmosphere south of the border - in El Salvador and the whole of Central America, as well as Mexico. In it Buckley suggests, not just that Washington has failed to learn from its past mistakes, but that the mistakes become grander, more expensive, and more tragic as time goes on.

Buckley is a former New York Times staff reporter, whose beats included Vietnam during the two decades of war there. Scenes from the past recur to him as he surveys the present predicament in Central America. He mixes on-site interviews with historical sketches of the violence and corruption he finds endemic to the region - Costa Rica being the sole possible exception.

Internecine rivalry and warfare have done much to divide Central America, he says. In 1969, for example, Honduras and El Salvador waged a brief but bloody ''Football War,'' caused in part by the former's mistreatment of the latter's national soccer team. What internal strife has not done, Buckley argues, US interventions of many sorts have done.

Selective interpretations of the Monroe Doctrine by various US administrations (Teddy Roosevelt perhaps applied it the most forcefully during what came to be the Panama Canal negotiations) became almost synonymous with ''send in the Marines.'' That strategy worked, or seemed to for a time. The trouble is that Procrustean means no longer provide even short-term remedies for chronic injustices. The corruption engaged in by professional armies or officer corps has only been worsened by the largess of US aid, Buckley argues.

The author is careful to avoid hand-wringing, knee-jerking cliches. He finds, for example, that United Brands, the scaled-down offspring of the infamous United Fruit Company, is regarded as a model of employer decency even by leftists in the region: tolerance of unions, employee medical facilities, and day-care centers set United Brands apart from other companies.

Buckley's droll wit works best in pointing up sad ironies. In El Salvador, he finds that many of the problems afflicting Jose Napoleon Duarte result from Mr. Duarte's honesty. (Duarte, of course, is the leading Christian Democrat and the man many Americans would prefer to see in office after El Salvador's run-off election next month.) In 1972, when by all accounts Duarte had won a presidential election, the opposition and the military forced him out. Duarte, Buckley opines, had enough popular support to have seized power then, but he chose not to because he believed in the democratic process and its ultimate triumph. He was later jailed and tortured, and neither he nor his party has held sway since.

In Nicaragua, Buckley speaks with the at times harried and at times suppressed editor of La Prensa, the opposition press, who tells him that the Reagan administration's policies intended to weaken the Sandinistas only help to reinforce their rule. Buckley notes that he feels secure walking after dark in Managua, Nicaragua - but not in either El Salvador or Guatemala.

His chapter on the relationship between Mexico's fiscal woes and its stance toward the policies on Central America indicates just how intertwined the region's politics are.

If I have a complaint with this book, it is that perhaps Buckley throws too wide a net. His experience as a reporter apparently made him rely mainly on ''facts'' and anecdotes, rather than drawing a more impressionistic depiction like the one found in Joan Didion's ''Salvador.'' When Buckley does write impressionistically, as when he describes coming across two dead Indians slumped in the branches of a tree in Guatemala, the effect is stunning.

But these are minor cavils with a book whose message is unmistakable: Here we go again with a strategy of pouring US money into corrupt governments, a strategy that in the past has left a handful of men shamefully rich and the peasantry shamefully poor. The result is likely to be a regional morass whose legacy can only be more resentment, bitterness, and death.

''Violent Neighbors'' goes far to show that what backfired before can blow up again - and again and again.