DETROIT (AP) — Tesla Inc. is balking at recalling about 159,000 vehicles with potentially defective touch screens. So U.S. safety regulators are moving to force the company to take action. The National Highway Traffic Safety Administration on Wednesday sent a letter to Tesla saying it has tentatively determined that the screens are defective and pose a safety risk. The agency says the backup cameras can go dark and the defrosters can fail. It wouldn’t comment beyond the letter, which is a rare step toward a public hearing and eventual legal action. Experts say the letter means that Tesla has resisted doing a recall that NHTSA feels is necessary. Messages were left Wednesday seeking comment from the electric vehicle maker.