So you want to be a reporter? Start writing!

Stephen Buckley's dream to become a newspaper reporter was nudged a little closer to reality this summer in an integrated training program with an emphasis on finding talented young minority students and pointing them toward careers in journalism.

Stephen, 15, was one of the dozen black students in a six-week internship program sponsored annually by Modern Media Institute (MMI), an educational foundation for journalism training at all levels, from students to top professionals.

Stephen and his colleagues imitated the real thing by attending a press conference held by Florida Gov. Robert Graham; sitting in on editorial board meetings at the St. Petersburg Times and the evening Independent; touring senior recreation centers and rehabilitation homes to write a story on aging; exploring the Salvador Dali Museum; and turning out stories on deadline.

''It was fantastic,'' Stephen said. ''It made me want even more to be a journalist because now I've seen the fulfillment when, for instance, you interview someone who is lonely and get that person to talk and share feelings that have been pent up for a long time. It's an eye-opener.''

The students wrote under the tutelage of Dr. Roy Peter Clark, often called the guru of good newspaper teaching and writing for his pioneer efforts, first as a writing coach at the St. Petersburg Times and currently as the head of MMI's Writing Center, offering innovative seminars for editors, reporters, college and high school students.

Dr. Clark's fresh approach to The high school students especially responded to his warmth and wit. When one class lined up on the first day around a table with all the white students on one side, the minority students on the other, he quipped: ''Am I going to have to bus some people across the table?'' Laughter eased the tensions and the group went on to publish an impressive series of first-person experiences ''riding the bus'' during the first decade of integration in their community.

''We find that working on a school newspaper is often primarily a social activity,'' Dr. Clark said, ''and as a result, minority students are often excluded. One of the effects of our program has been to introduce minority students to local high school newspaper staffs.''

The other impulse, he added, is to ''identify talented minority students at an early age and help them work their way through school, help them with their writing, and introduce them to the world of journalism.''

MMI's tuition-free High School Internship Program awards each participant a $ 360 fellowship ($60 weekly), so students earn as they learn. Otherwise, many could not take advantage of the program because of the need for summer income.

Students are recruited early in the year through visits to high schools in the St. Petersburg area and in cooperation with minority community and business leaders. Eighteen are selected to attend five Saturday morning sessions in the spring to acquaint them with journalism and develop their writing skills.

Dr. Clark draws upon the most outstanding students in this group for the summer internships. Once in the MMI fold, he maintains continuing relationships with them during their high school and college years, offering help with their writing and their educational plans.

Dr. Clark has been assisted for the past two summers by Vivian Rouson-Gossett , a high school teacher, newspaper columnist, and integration leader in Florida's black community. She is now a resident of Burnsville, Minn.

Jill Corson, 17, of Countryside High School in Clearwater, said of this year's course: ''It gave me a head start on a career. I feel better prepared to enter college as a journalism major.'' Julia McMillian, 16, of Osceola High School in Seminole, says: ''It gave me an exposure to the world of journalism and improved my writing.'' Both students have won awards for their school newspapers.

Other MMI programs which serve the cause of better high school journalism:

* Students from 18 public and private high schools in Pinellas County produce their newspapers in MMI's modern type lab. More than 1,000 students have been trained to operate video display terminals, headliners, and other equipment.

* Workshops are conducted throughout the school year for school newspaper staff members and their advisers.

* A college credit course for newspaper and yearbook advisers is held at MMI during the first two weeks of the University of Southern Florida summer session.

MMI director Donald K. Baldwin stresses the special importance of the High School Internship Program as part of MMI's dedication to increasing minority participation on the staffs of the nation's newspapers. By training gifted minority students early, there will be a pool to draw upon when their educations are complete.