BRASILIA, Aug 27 (Reuters) - A group of about 150 indigenous people protested in front of Brazil"s presidential palace on Friday, setting fire to a giant coffin that had been carried in a demonstration ahead of a landmark Supreme Court ruling over their ancestral lands. The group was a small part of the roughly 6,000 indigenous people from 176 tribes that have descended on the capital to denounce a proposal setting a cut-off date of 1988 for their land claims. Billows of black smoke rose from the flaming coffin in front of the palace, as protesters - many in traditional dress - shouted and chanted while soldiers stood guard nearby. Originally slated for earlier this week, the Supreme Court on Thursday pushed the ruling to next week, saying it would reconvene on Wednesday to take up the case. The ruling will affect hundreds of pending land claims, many of which offer a bulwark against deforestation in the Amazon rainforest. Most have been awaiting recognition for decades. The case rose to the Supreme Court in an appeal by the Xokleng people - driven from their land in the southern Santa Catarina state over a century ago. The Xokleng have challenged what they call the state"s overly narrow interpretation of indigenous rights, recognizing only lands occupied by native communities when Brazil"s constitution was ratified in 1988. A defeat in court for the Xokleng could set a precedent for the dramatic rollback of native rights which far-right President Jair Bolsonaro advocates. He says too few of them live on too much land, blocking agricultural expansion. Powerful farming interests would have firmer legal ground to challenge indigenous land claims and Congress would have the green light to write a restrictive definition of indigenous lands into federal law.