EL RENO, Oklahoma -- Halliburton is laying off more than 800 employees in El Reno, Oklahoma, and says it expects to close its office in the Oklahoma City suburb.The move by the Houston-based company is expected to have limited impact, if any, in Texas. Companies are required to file advance notice for large layoffs in Texas, and none has been filed by Halliburton in recent months.Oklahoma Office of Workforce Development spokesman David Crow says the agency was notified of the layoffs and apparent closure of the office, effective Monday.A Halliburton Energy Services Inc. spokeswoman tells The Associated Press the company will provide additional information "by midday" Tuesday.Crow provided a letter from Houston-based Halliburton, dated Monday, that says the "mass layoff" of 808 employees is expected to be permanent and that "at this time it is expected that the facility will not remain open."He says the letter was the first the agency had heard of the pending layoffs and office closure.