David L. Sobel's strictures {letters, July 29} stimulated by my op-ed reminiscence on the CIA's relationship with the National Student Association {op-ed, July 19} are only semivalid. The CIA's covert subsidy of the NSA, dating back to 1952, was wrong, and President Johnson properly put a stop to it when I reported this to him in early February 1967. Perhaps I was overly sanguine in remembering that the CIA had not done fundamental damage to a vigorous student organization whose leaders never hesitated to criticize U.S. foreign policy whenever they saw fit. It is a sad fact of life, I noted, that Congress shows little interest in providing overt funding for international outreach by voluntary associations that other countries freely subsidize.

What damage was inflicted on the NSA? Both NSA's supervisory board and, a decade later, the Church Committee used speculative language when referring to contaminating influences. Yet I agree with the Church Committee conclusion: ''The Central Intelligence Agency's experience with the NSA underlines the basic problem of an action-oriented clandestine organization entering into a covert funding relationship with private organizations: support of friends turns into control of their actions and ultimately to creation of new 'friends.' ''

As one who worked to found the NSA when it led a bare-bones existence without prospect of governmental assistance, covert or overt, I can only conclude that the NSA officers were both mindless and greedy when they accepted subsidy that, by its supervisory board's own estimate, amounted at one period to 80 percent of the (student) organization's budget. Surely someone should have grown suspicious of where all that money was coming from.

Mr. Sobel enters ticklish territory when he discusses the relationship of an intelligence agency with individual student leaders. The CIA, like the Office of Strategic Services, which I served for a time during World War II, has had a tradition of attracting a good many highly worthy young people into its employ where they must cope with the murky dilemmas of intelligence and counterintelligence. I, for one, hope that the agency's misdeeds and misadventures do not slam shut the door for high-minded and highly ethical recruits in the future.

DOUGLASS CATER President, Washington College Chestertown, Md.