ARCHEOLOGISTS have tried. Students of ancient climate and ecology have tried, too. But no one has yet come up with a satisfactory answer: Where did Hannibal get the elephants for his heroic march across the Alps to attack the homeland of the Romans?

The question was raised anew in the Sept. 6 issue of New Scientist, a British magazine. Derek Ager, a geologist, wrote an article casting doubt on all of the proposed sources of Hannibal's elephants.

Once there were elephants nearly everywhere, but by the time of Hannibal's march in 218 B.C. they had already dwindled to the two species extant today, the Indian, or Asian, elephants and the African ones.

If he had had a choice, Hannibal would presumably have gone into battle with Indian elephants, which had been used effectively a century before in charging against the forces of Alexander the Great. Indian elephants are not quite as large as the African species but much more easily trained, which is why they are favored by zoos and circuses. It is also the reason Indian elephants are seen tramping through fictional Africa in old Tarzan movies.