WORLD LEADERS converged on Sarajevo last week to pledge a Balkan renaissance, promising to rebuild Kosovo and suggesting the economic development might help neutralize ancient hatreds. As part of the process, the rebuilders ought to spare some effort for mapping -- and, where possible, reversing -- the harm done to Kosovo's cultural heritage. As in Bosnia and Croatia, those bent on "ethnic cleansing" often sought to erase monuments, archives and libraries that marked centuries of the victims' history in the area. Observers say historic city centers and 15th- and 16th-century mosques were burned and bulldozed in the cities of Pec, Djakovica, Vucitrn and others. Many of the ruins are mined.

Wartime propaganda from Belgrade accused NATO of targeting the region's celebrated Serbian Orthodox cathedrals and monasteries -- part of the heritage invoked in Serbian rhetoric as the basis for territorial claims. Observers say there is no evidence that those buildings suffered visible damage, but since the war's end there have been disquieting incidents of vandalism by KLA forces at Serbian sites, along with other reprisals. Secretary of State Madeleine Albright rightly condemned such continued attacks.

But the lesser-known heritage of six centuries of Muslim Ottoman rule appears to have suffered the most systematic "cleansing" -- much during the war, some under the prior decade of Serbian administration. The National Library in Pristina saw the removal and apparent pulping of 100,000 of its 600,000 volumes under Serbian authority in the mid-1990s. Preservationists plead for the chance at least to document the ruins "before someone starts carting away the stones," as one put it.

The Bosnian experience offers some warnings. New housing built hurriedly in city centers could eradicate more heritage. In Bosnia, some mosques were rebuilt with funds from conservative Islamic regimes that obliterated historical features they disapproved of. With so much urgent humanitarian work to be done, the claims of heritage have trouble getting a hearing. In the wake of such targeted destruction of a culture, though, they ought not be forgotten.