Loews Corp., the movie-theater operator and cigarette manufacturer, asked the Securities and Exchange Commission yesterday for permission to raise its stake in CBS Inc. to as much as 15 percent. CBS said "it accepts on good faith Loews' statement that these stock purchases are for investment" and had no further comment.

Last week, Atlanta cable television enterpreneur Ted Turner ended his hostile $5.41 billion bid to acquire CBS with high-risk "junk" bonds after the network virtually killed his proposal by accepting about 6.4 million of its own shares under a buy-back offer.

Sources said Loews previously has indicated to CBS it would be interested in acting as a "white knight," or friendly acquirer, in the event CBS becomes the target of a viable hostile takeover bid. They said Loew's announcement yesterday indicates it either wants to position itself as the most likely white knight or as a significant investor that can later sell its CBS shares for a premium price.

On July 29, Loews disclosed that it had bought 9.9 percent of CBS' outstanding stock. Loews then tendered those shares to CBS, but the network's buy-back offer was oversubscribed and not all of Loews' holdings were accepted for payment. Under the Hart-Scott-Rodino Act, Loews must wait 30 days before resuming purchases of CBS stock.