The following letter, translated from Russian, was written by Yelena Bonner for the Associated Press shortly before she began her return trip yesterday to the Soviet Union.

I am leaving America today. I have spent six months here with my mother, my children and my grandchildren. It was here that I experienced one of the miracles of the 20th century -- a sextuple bypass which restored me to life. There will be much to remember. I am grateful to my doctors. I am grateful to my husband's colleagues who received me in Boston, New York, Washington and California. I am grateful to the hundreds of Americans who expressed their concern and compassion in letters and in person.

I am returning to my husband in Gorki. There, I have another four years in exile to serve or perhaps much more than that. Like my husband, I will not be allowed to leave the city limits, or meet or speak with anyone. It is hard to return to a life without freedom. It will be hard once again to accustom myself to a policeman at my door, to being openly followed on the street, to a life in which hidden cameras and microphones are trained on us.

But, most of all, I am afraid that once again we will find ourselves in utter isolation, deprived of communication with my children, and the world in general. I am afraid that once again the sole source of information about us will be films made by hidden cameras to show you how happy we are in Gorki. I am afraid that my children and friends will once again begin to receive forged telegrams and postcards supposedly from us.

I want you to know that on the first Monday of every month, my husband and I will go to the local post office and await a call from our children. I ask everyone concerned with the fate of Andrei Sakharov and myself not to believe any reports about us if they have not been confirmed in a telephone conversation with our children.

My doctors consider it necessary that I return to Boston for observation in a year or, at most, two. I would be very glad to return, but that does not depend on me alone but on the Soviet authorities, and on you as well.