Smartflex Systems Inc. of Tustin, an electronics parts maker, said it has agreed to be bought for about $67.9 million by closely held Saturn Electronics & Engineering Inc. of Auburn Hills, Mich. Saturn makes electronic systems and parts for the automotive, defense and other industries. Saturn will pay $10.50 for each of Smartflex's 6.4 million shares outstanding, more than double Tuesday's closing price of $5.03. Smartflex stock rose $4.53 to close at $9.56 on Nasdaq. A Smartflex spokesman, John Hohener, said he "guessed" Smartflex factories wouldn't be closed. Smartflex revenue fell 19% to $107 million in 1998 from $133.3 million in 1997. Saturn expects to make the tender offer by Wednesday.