At the risk of sounding defensive, I feel compelled to respond to the July 18 article by Spencer Rich titled ''GAO Faults Social Security '800' Hotline.'' The article creates the mistaken impression that ''a substantial proportion'' of callers to Social Security's 800 number are not receiving good public service. The General Accounting Office study draws no such conclusion, and nothing could be further from the truth.

GAO estimates that the Social Security Administration receives 70 million calls annually on its toll-free number and states plainly that most are handled to completion with the very first phone call. About 3 million of those 70 million annual calls are referred to local field offices for resolution. The local offices then contact the caller to set up an appointment or otherwise resolve the problem.

GAO surveyed roughly 600 of the 3 million persons referred to SSA field offices to determine if Social Security had recontacted them. In one category, GAO found that the field office did not make contact 11 percent of the time. Two other categories revealed unsuccessful phone recontact rates of 24 and 42 percent.

What do these numbers really mean? They mean that in less than 1 percent of all calls to our 800 number, SSA was unable to recontact a caller by phone. This 1 percent -- 0.97 percent to be exact -- is hardly the ''substantial portion'' the article suggests.

GAO itself experienced significant difficulties in reaching the study participants by phone. Most important, however, GAO acknowledged that in those instances when Social Security is unable to recontact the caller by phone, operating procedures instruct the local office to correspond with the caller by mail. This ensures that no one who contacts us falls between the cracks simply because Social Security is unable to reach him by phone. The article fails to mention that GAO never checked survey participants to determine if they received a letter when they were not contacted by phone.

I am perplexed therefore by critics alleging that ''the 800 number is not a working number.'' The GAO study does not draw this conclusion. Instead, it focuses on work assigned to SSA field offices. Our 800 number system has been in operation nationally for the past 10 months, and our studies indicate the public is not only satisfied with this service but increasingly prefers it as a means of conducting Social Security business.

The system is still new, and we are continuing to improve it. We regularly monitor the quality of our service to ensure that the public is not only being served but is being served well. I remain committed to this self-assessment, as well as to specific recommendations made by GAO and others, in order to make this telephone network the model system the American public deserves.

GWENDOLYN S. KING Commissioner of Social Security Baltimore