Her body was found near a bandstand at Weymouth pier in Dorset by three men who were metal detecting on the beach on 15 October 1981.
Investigators have urged her mother and father to come forward as they can now get a DNA profile of the baby.
Police said the profile will take "several months" to complete.
The girl's body was inside a white carrier bag which was in a larger canvas bag found just above the high waterline of the beach, the force said.
The carrier bag had printed on its side: "Bath Street Wine Cellar, Quality Wine Merchant, Jersey CI."
Crime review officer, Phil James, who is leading the cold case investigation, said: "Dorset Police has a duty to bring this unsolved historic case to a conclusion and is committed to doing so.
"I would appeal to the mother or father of the baby to contact me.
"They may be keen to bring closure to this very sad case and may wish to do this with some dignity, rather than live in fear of receiving that unexpected call.
"Advances in forensic science now provide investigative opportunities to obtain a DNA profile of the baby girl and, potentially, the mother and father.
"This detailed examination work has started and will take several months."
Referred to by the media at the time as the ‘Baby on the Beach’ case, the little girl’s body was found on the beach near to Weymouth’s pier bandstand by three men as they were metal detecting on 15 October, 1981.
Despite extensive enquiries at the time, detectives were unable to establish how the carrier bag came to be on Weymouth beach but one theory was that it may have been thrown from the ferry between Weymouth and Jersey in the Channel Islands.
The circumstances surrounding the baby girl’s death have never been determined and now the ‘cold case’ is being re-examined by Dorset Police’s crime review officer Phil James, a former Detective Superintendent with the force.
Phil James said: “If anyone has information that could help my enquiries, I am very keen to hear from them. All calls will be treated in the strictest confidence and I am interested in any information – no matter how unimportant or irrelevant people may believe it to be.”
Witnesses and anyone with information should contact Dorset Police