In her piece "Can We Now Trust the Sandinistas?'' {op-ed, Sept. 28}, Jeane Kirkpatrick wonders if recent concessions by Nicaragua's leaders are sincere, or merely a case of ''Lenin's recommended tactic of 'two steps forward, one step back.'''

In fact, Lenin's 1904 tract was titled ''One Step Forward, Two Steps Back.'' Moreover, it was not a ''tactic'' for Communist advancement but rather a lament over the infighting that had plagued the Russian Social-Democrats since their second party congress in 1903.

It comes as no surprise that anyone affiliated with the Reagan administration should misquote or misinterpret the words of Vladimir Lenin. The president himself has frequently quoted ''Nikolai'' Lenin, and one of his favorite quotations (often cited in support of his Nicaraguan policy) is Vladimir Lenin's supposed ''prophecy'' that after gradually encircling the United States, ''We will not have to attack: it will fall into our hands like overripe fruit.'' Rather than appearing in any of Lenin's works, this quotation has been traced to an early publication of the John Birch Society.

But shouldn't we expect more from Prof. Kirkpatrick, the author, among other books, of ''The Strategy of Deception: A Study in Worldwide Communist Tactics''? Lest this seem like just an academic quibble, remember that the difference between Prof. Kirkpatrick's misquotation and the original is that in one case the Communist Party advances, while in the other it retreats. ROBERT ENGLISH Department of Politics, Princeton University Princeton, N.J.