Two former executives of Texaco, Inc., who had been taped discussing the destruction of documents demanded in a racial discrimination lawsuit against the company were found not guilty yesterday on charges they tried to obstruct justice. Lawyers for Richard Lundwall, the man who secretly recorded the meetings, and Robert Ulrich, the former treasurer of the big oil company, said the acquittals vindicated their arguments that the two had done nothing illegal. But the verdict by the jury of eight men and four women in a federal court in White Plains stunned and angered civil rights leaders who said it was based on technicalities and sent a disturbing message about permissible behavior by corporate officers.