ROBERT GATES, President Bush's nominee to head the Central Intelligence Agency, appears to have undergone a "confirmation conversion" of his own this week. In contrast to his testimony in 1987, the first time he was nominated for the post, Mr. Gates now remorsefully acknowledges that he may have been insufficiently attentive to the developing Iran-contra scandal as its tentacles began to creep into the CIA when he was the agency's deputy director.That mea culpa is welcome. Still, one has a disquieting sense that Gates is being evasive in his recollections of his actions in regard to Iran-contra. For an analyst famed for his tough brilliance and retentive memory, Gates has been surprisingly unable to recall many events of the period. Nonetheless, unless a smoking gun proves that Gates was knowingly involved in either the contra-supply affair or its coverup, he should not be disqualified from confirmation on that basis alone. If his awareness of the matter was as sketchy and indirect as he says, it's unreasonable to expect him to have blown a whistle. Other issues, however, raise questions about Gates's fitness. Did he tailor CIA intelligence estimates to fit Reagan administration policy objectives? Did he break the law in providing Iraq with satellite intelligence during its war with Iran? Such questions, because they involve classified information, must be probed behind closed doors, but the Senate Intelligence Committee should examine them closely. No one questions Gates's expertise in intelligence matters, the fruit of three decades in the field. Paradoxically, however, that very depth of experience raises another issue. Is it desirable for a longtime employee of the CIA to become the boss, especially at a time of great flux in US intelligence gathering? Or would the intelligence community benefit from new blood - a fresh, disinterested leader who, though having wide government experience, is not steeped in the CIA's parochial culture, has no stak e in the status quo, and has invested no personal capital in current policies and practices? Adm. Stansfield Turner, President Carter's CIA chief, and outgoing chief William Webster brought fresh thinking and values to the spy agency, with healthy results. With the end of the cold war and a shrinking budget, the CIA has to rethink its mission and redeploy assets. The new director of central intelligence will have to be a reformer. Gates declares himself just such a reformer, but will his long institutional ties be an impediment?