The agreement would come more than a year after Texaco's board rejected a formal proposal from Chevron to acquire it for about $37.5 billion, citing unacceptable ''complexity, feasibility, risk and price'' as the reasons for abandoning the deal. The real stumbling block to that deal has been removed: Chevron's then-chairman and chief executive, Kenneth T. Derr, retired. He had demanded that a Chevron executive head the new company, according to people involved in the talks then.