Your first test at State U.: finding a way to get along with freshman No. 76948

College freshman No. 88503 has been sent her roommate assignment, and she is already wondering what it will be like to share a closet, towel rack, and wastebasket with freshman No. 76948.

Fortunately, the information packet also includes the name, address, and telephone number of her prospective roommate, so Mary (88503) has talked with Susan (76948) on the phone. Now both know who will bring a stereo, who a carpet and fan, and when each will arrive on campus.

The first test, the first term paper, even the first big dance will all come later, but getting along with a college roommate is a job that begins on day one , or in the case of Susan and Mary, even before that. Finding common ground needn't be difficult, but challenges often present themselves.

When David Poole was a sophomore at North Carolina University at Chapel Hill, he learned about the three c's which contribute to a successful roommateship: communication, cooperation, and compromise. After several heated debates over carpool schedules between their house and campus, the roommates began to recognize and appreciate each other's values. They agreed to forgo their rush home to watch Andy Griffith reruns and, David admits, ''taught me to relax and enjoy myself more.''

What happens if roommates just don't get along? During their first semester at college, Holly Wilder and her roommate reached a point where they refused to speak to each other. Holly sought the help of her guidance counselor. (Most colleges have personnel trained to handle such complaints.)

''It helped to talk things out,'' Holly said, ''and the counselor told me that if things didn't improve we could switch roommates at the end of the semester. She also encouraged me to be more flexible and to explain to my roommate how I felt. I did talk with her, and after that my roommate and I tried to be more cordial. We were never great friends, but we got along.''

The toughest problems for roommates to resolve, college students say, are those where moral issues are involved. A student could let his new roommate know when they first meet - and before the roommate's girlfriend arrives for the weekend, for example - that overnight coed visits, or drug use, or alcohol abuse are morally unacceptable to him. If the morals of one offend the other, a transfer can often be requested. When a young woman learned that her roommate was lesbian, she asked for and immediately received a new room assignment. Though many universities and colleges say that they do not assume parental responsibilities, most will help a student stuck in a situation where moral standards are involved.

Karen Bloom, the administrative assistant to the dean of students at Middlebury College in Vermont, is in charge of matching up roommates and handling complaints during the year. Karen urges prospective students to be as specific as possible when asked about their rooming preferences. ''So often I read comments like 'I work hard and I play hard.' Great. But how does that help me to match them up with a compatible roommate?''

Numerous colleges and universities allow students to choose between coed or non-coed housing, quiet dormitories, or foreign language houses.

At Colby College in Waterville, Maine, students can request to live on special-interest floors with other students who are art majors or pursuing subjects like women's issues. By requesting to live in a special-purpose residence, students are apt to meet others who share their interests and ambitions.

Penny Wills, director of residential programs at Reed College in Portland, Ore., feels that conflicts can be avoided if roommates ''take the time to get to know each other and to get over first impressions and stereotypes.''

To friends, counselors, or parents who are trying to help incompatible roommates get along better, Ms. Wills offers some ideas that have worked for her:

* Encourage both students to sit down and talk with each other.

* Before they talk, have them write down every single complaint they have. Often when they see the list, they will recognize some as too petty.

* Most roommate problems are resolvable, and the process of solving problems teaches students how to handle disagreements or anger and how to get along with all types of people.

Is having a roommate worth the effort?

''Sure is!'' says a student at Kansas University. ''I have six of them and I love it.''

He spent his first two years of college in a fraternity and valued the sense of camaraderie that developed between the men in his house.

Are there any disadvantages to living in a fraternity?

''Well, we had a community closet. I don't know whose clothes I wore all year , but they weren't mine. If my younger brother were going to college, I'd give him one piece of advice: Put name tags in your shirts.''

The University of Rochester prints a service bulletin entitled ''Getting Along With Your College Roommate,'' which includes practical suggestions for a successful roommate-ship. Single copies of the pamphlet are available on request from Department RM, Office of University of Communications, University of Rochester, Rochester, N.Y. 14627. Enclose a self-addressed stamped envelope with your request.