I have taught music at Columbia University, Stanford University, Queens College CUNY, San Francisco State, and the University of Kentucky (composition, harmony, counterpoint, computer music, ear training, orchestration, arranging, music education, music history, etc). My wife has taught voice at Stanford, the University of Kentucky, and is currently a tenured professor of voice at the University of North Texas. She has a career as an opera singer and has made over 40 commercially released CDs and several DVDs. I have been around academia, composers, and professional performers since 1968. I am now a public school music teacher. I teach little kids. I am a bassist and composer. I also teach violin, play guitar and piano, sing, and compose vocal music, chamber music, orchestral music, and computer music. Sorry about the "freeze-dried" resume, but I thought you ought to know where I get my opinions.
In the U.S., if you enter a B.M. (Bachelor of Music) program, you will have to undertake performance study, no matter what your major. There are very few or even zero exceptions to this. There are national standards that mandate curriculum. The B.A. (Bachelor of Arts) degree is less demanding, but will also have some performance requirements. Essentially all worthwhile programs demand you study an "applied" instrument.
IMHO, this is as it should be. The greatest weakness a composer can possibly have is to be an armchair musician. It will isolate you from the very people you will need to be thinking about and dealing with every day: professional performers. Furthermore, it will isolate you far too much from your major source of knowledge: musical scores as they emerge into reality through performance. Score reading is not performance, nor is listening. It seems silly to say this, but the demands of music are unyielding and unchanging across the centuries. You must see and hear music as a performer to be an effective composer.
IMHO, there is no such thing as a person who is "just a composer." If you cannot articulate music in a significantly professional way on an instrument, you are doomed to be a hobby composer. Performers and other composers won't respect your work because of the inevitable (and obvious) resultant weaknesses. You simply will not get it. You will not be able to enter into musical creation in a fully realized way. Don't believe me, ask any professional musician who deals with young composers.
BTW, you may find that some courses and (more crucially) ensembles for performance of your work are unavailable to you if you are not a B.M. composition student. All Music programs are most interested in those who will excel and "rain glory" down upon their Alma Mater. They rightfully pour their limited treasure into those students. It is not a democracy, it is the jungle. I am not joking.
Even if you have no desire to become a University instructor, you will discover that most schools with significant reputations for music composition study (with the possible exception of a few Jazz programs) reserve access to the "famous composer/professors," to graduate students. That is those who have finished a B.M. or B.A. and are pursuing a M.M. (Masters of Music), M.A. (Master of Arts), D.M.A (Doctor of Musical Arts), or PhD. As a result, you will study with the students of the professors, the graduate students.
If you enter a graduate program, performance matters less, but those who can seriously get around on the their primary instrument AND piano are going to be taken much more seriously by teachers. Why? Because those performance skills translate into greater insight into composition. How come? Because performers simply know much more music well, can more clearly and artfully imagine and notate their ideas, and have a deeper connection to expression. Sorry. It's true.
My advice: Since I presume you are an electric bass player, start studying double bass and piano. While doing so, start composing music for these instruments, music that YOU can play. Notate it, play it and record it. It will help you a lot.
Admission to a music program in the US is pretty assured to a foreign student with some good skills on electric bass, some foundation in double bass and piano, and a portfolio of compositions. Also, if you have sung in choirs and can read well, find a way to show that.
There are a lot of great programs here, I hope you find one that fits.
