openssh rsa encrypt problem

On Linux FC4, I am trying to use openssl to encrypt messages.
Here is my script:

openssl rsautl -in $1.txt -out $1.crp \
-inkey public_key -pubin -encrypt

It works for small input files, but for an input
file of length 286 bytes I get:

RSA operation error
27358:error:0406D06E:rsa routines:RSA_padding_add_PKCS1_type_2:data too
large for key size:rsa_pk1.c:151:

Is there something I can do about this? I would hope it
is possible to encrypt large messages.

If there is a better place to ask this, please let me know.

Thanks for your help.