This story was published in the mid-1970s, probably in F&SF, I remember it in a magazine, not in a book. It is told from the perspective of a U.S. military unmanned, artificial-intelligence starship with a smart-aleck personality, launched as part of an international armada (he complains about Russian ships and their Cyrillic alphabet) to fight a malevolent alien force for which he has a dismissive nickname, like "spacelees" or something. He is orbiting 1970s Earth (supposed to be ours). He has difficulty making contact as the U.S. space program has been shut down and its facilities are now museums. Just by luck museum staff were monitoring the radio. He then realizes not only is he in the past, but in an alternate timeline -- he refers to the U.S. founding fathers, "Washington, Jefferson, Madison, and our first president, Schwartz," (or something like that) and is surprised when the USA he is talking to has a different history (ours). He then realizes that this non-spacefaring Earth will be a sitting duck for the aliens and must decide what to do.
I believe the story in question is "Helbent 4" by Steven Robinet "I was programmed by the NASA contingent. They speak English, I speak English. Never did get along with those Ruskie-speaking ships."
Here are the covers: http://www.isfdb.org/cgi-bin/titlecovers.cgi?51699