ATLANTA (AP) _ A graphic British television film about a fictional nuclear attack will be shown the week of Jan. 13 by the Turner Broadcasting System Inc., which is promoting the program with a crusader's fervor.

The film, ''Threads,'' will make its American debut Sunday night on Ted Turner's WTBS cable station, followed Monday by a documentary about the effects of the so-called ''nuclear winter'' and a panel discussion on the dangers of nuclear war. In all, WTBS will devote 41/2 hours to the subject over the two nights.

''No one is immune to the threat of nuclear destruction,'' said Turner, chairman of the WTBS board and head of Cable News Network. ''By airing programs like 'Threads' and (the documentary) 'On the 8th Day,' it's my intention to increase the public's consciousness of the potential dangers of nuclear proliferation.

''I dream of a future when our children will be free from the fear of world destruction,'' Turner said.

The film, which the BBC first broadcast last September, is set in the industrial town of Sheffield, England. Focusing on two families, the story depicts an attack on Britain resulting from a war between the United States and the Soviet Union.

The drama follows the events leading to the attack, and its aftermath through 13 years.

The two-hour film, which is said to be much more explicit than last year's American-produced television broadcast ''The Day After,'' has had less than a minute cut from the original version for its broadcast in the United States, said Robert Wussler, executive vice president of TBS.

''There were a couple of scenes a little more graphic than we wanted to show, and didn't really add to the story,'' Wussler said.

Still, the movie may prove to be too much for some viewers. WTBS will air warnings that some viewers may be offended and that children should not watch the program alone.

The station will have about six people handling expected telephone calls from viewers Sunday night, said TBS spokesman Mike Oglesby.

''I think some of the audience will turn it off,'' Wussler said. ''Anytime you run something like this, you run that risk.''

But he said the topic of the film demanded a graphic account.

''Obviously, there will be a point of view in the broadcast,'' Wussler said. ''And it's very much a point of view that something must be done about this foolish, upward spiraling (of the arms race).''

He said the film, a week after the arms talks in Geneva, Switzerland, between U.S. Secretary of State George Shultz and Soviet Foreign Minister Andrei Gromyko, was a coincidence. The programs were scheduled about three months ago.

''Threads'' will be shown on WTBS Sunday at 8 p.m. EST. It will be repeated Jan. 23 and Jan. 27. ''On the 8th Day'' will be shown Monday at 8 p.m. and repeated Jan. 24 and Jan. 27. The panel discussion, featuring astronomer Carl Sagan and others, will be shown Monday at 9:05 p.m. and repeated Jan. 24 and Jan. 27.