SHREVEPORT La. — After a 45-minute discussion about computer programming with a group of high school students, the sales pitch begins.

LSU-Shreveport assistant professor Marjan Trutschl switches the slide on his presentation. Pictures of an iPhone, a Blackberry and the Google logo with the words ‘‘try to imagine a world without programs’’ are projected on the screen in front of the classroom.

‘‘If I haven’t convinced you that computer programing is important, imagine your life without this,’’ he said, pointing to the screen.

The students perked up. Trutschl continued, presenting a video about the advances in science because of a super computer, a story about one of his student workers who started taking classes at 12 years old and a handout detailing the top 10 reasons to major in computing.

‘‘If you want to make a difference, this is one of the ways to make a difference in the world,’’ Trutschl said. ‘‘You can expect to make a good living.’’

The sales pitch is designed to get students interested in jobs in computer science to help buck a national trend. According to the federal Bureau of Labor Statistics, jobs related to computer science and networking are the fastest growing careers; however, nationally, there are fewer students entering college programs.

John Sigle, a professor and chairman of LSUS’ computer science program, has seen the trend at the university. Since the 2002-03 academic year, the number of degrees conferred by LSUS in computer science has decreased steadily. In that academic year, 22 degrees were awarded. By 2006-07, the latest year for which information is available, eight degrees were conferred.

Other universities have experienced similar patterns. University of Louisiana at Monroe conferred six computer science degrees in 2002-03 and three in 2006-07. Louisiana Tech in Ruston conferred 25 in 2002-03 and 20 in 2006-07, after a yo-yo-ing in the number of degrees.

The nation has seen a 50 percent drop in computer science enrollment programs since 2001, Sigle said. He helped establish an annual summer event, CSI: Careers in Science Investigations, in part to help combat the problem.

‘‘Not enough students are entering the major. We’re just doing what we can. We’ll call it a success if we get a handful of people in the major that we didn’t have before.’’

The dot-com bust of 2001 probably soured people on the idea of computer-related careers, Sigle said. He also cites the outsourcing of computer jobs overseas.

But those explanations, he said, only go so far. ‘‘While there is a fair amount of outsourcing, there is so much need that there still is a shortage.’’

Trutschl offers another theory about why students are not entering computer science programs. ‘‘They flock to nonscience majors because it’s easier. They don’t understand that with work up front, you can see the fruits of their labor later.’’

Trutschl, who oversees one of the computer labs on campus with student lab workers, said the demand for computer science majors should make students want to at least consider it. ‘‘Our guys are getting hired before they graduate.’’

Students’ theories differ from their professors. Phillip Kilgore, who just received his undergraduate degree in computer science and will return in the fall for the master’s program, said the reason more students don’t enter computer science programs is they’re ill-prepared.

‘‘Students at the high school level aren’t being equipped for the college lifestyle,’’ he said.

Trey Wessler, a senior computer science major, agrees, adding that retaining students in the program also is a problem.

‘‘Even though enrollment is low, that isn’t the worst,’’ Wessler said. ‘‘The dropout rate is high. They go and get a liberal arts and business degrees. It’s a very difficult thing to stay with the program.’’

Sigle recognizes student retention is difficult but said it is part of a natural weeding out process. Not every student is cut out to be in computer science, he said.

‘‘We not only want to get people in (who) want to get in, but we want to get people out (who) need to get out,’’ he said. ‘‘We want students to succeed. I’m sorry to say that we get people (who) would not be good at it.’’