Atlanta media executive Ted Turner yesterday announced plans to acquire MGM/UA Entertainment Co. in a friendly $1.5 billion cash deal.

For Turner, the acquisition of the company based in Culver City, Calif., is an attempt to hold down the cost of obtaining programming for his WTBS-Superstation, the cable channel that broadcasts a variety of movies and sports to more than 30 million cable subscribers. It is also an effort to dramatically expand Turner Broadcasting System Inc.'s presence in the production and distribution of new programming. MGM/UA and Turner said jointly yesterday that they expect the deal to be completed by the fourth quarter of this year.

As a result of the size, timing and complexity of this transaction, it is unlikely that Turner can launch a serious attempt to gain control of CBS Inc. in the near future. After his initial hostile takeover bid for CBS died last week, Turner said he would attempt to devise a new plan to gain control of the company.

Sources involved in the negotiations said that, if the MGM/UA deal is completed, Turner will keep MGM assets, including the valuable MGM film library of 2,200 titles such as "Gone with the Wind" and "The Wizard of Oz"; the MGM film studio; 44 acres of real estate, and worldwide film distribution and syndication operations.

Turner immediately will sell United Artists' (UA's) assets to Kirk Kerkorian for $470 million. Kerkorian is currently MGM/UA's largest stockholder with 50.1 percent of the company. Kerkorian will acquire the 2,400-film UA library, which includes the successful "Rocky," "Pink Panther" and "James Bond" releases, and 50 percent interest in a company that distributes new releases. Kerkorian then will offer former MGM/UA shareholders the chance to buy stock in the new UA for the same price that he pays Turner.

"The proposed acquisition of MGM/UA presents a tremendous business opportunity for TBS and is an exceptional fit with our long-term business plans," Turner said yesterday.

"We think the acquisition of MGM/UA by TBS will be of great benefit to our shareholders," said MGM Chairman Frank Rothman. "The transaction, when coupled with the sale of United Artists and subsequent offer of United Artists stock to the former shareholders of MGM/UA, will enable our shareholders both to realize a substantial premium over historical trading prices for their MGM/UA stock and to continue, if they wish, in the motion picture business through United Artists."

MGM/UA stock closed yesterday at 22 5/8, up 4 3/4. Under terms of the proposed transaction, Turner will pay $29 a share in cash to MGM/UA stockholders, and MGM/UA will merge with a subsidiary of TBS. Then Kerkorian will pay Turner $470 million for UA, an amount equal to about $9 a share times the number of MGM/UA shares outstanding at the time of the proposed merger. Kerkorian then would sell stock in UA to those current MGM/UA shareholders who are interested for $9 a share.

The transaction is subject to the execution of a definitive merger agreement, approval of the boards of directors of MGM/UA and TBS, government approval and the approval of certain third parties.

MGM/UA lost $66.2 million on revenue of $478 million in the first nine months of its current fiscal year. In fiscal 1984, the company had revenue of $706.9 million and net income of $34.7 million.

Turner did not disclose yesterday how he would finance the transaction, but sources close to the negotiations said there were several viable options, including the sale of high-yield securities known as junk bonds. Drexel Burnham Lambert Inc., the undisputed leader in the sale of junk bonds, is advising MGM/UA in the transaction and could be instrumental in helping Turner to obtain financing.

Turner was not represented in the negotations by an investment banker. Instead, he relied on the outside advice of attorneys with the law firms of Latham & Watkins in Los Angeles and Troutman, Sanders in Atlanta.

Turner is not likely to renew his aggressive pursuit of CBS while he is trying to acquire and digest MGM/UA. A renewed Turner bid for CBS could make it difficult, if not impossible, to line up the financing required to complete the MGM/UA transaction.