Yes there is. If you're using the pserver, you specify it in the inet.d or xinet.d configuration. inet/xinet is the "superserver", which allows lightweight servers to be loaded and run dynamically without the need to keep a daemon process running full-time. In effect, the listener part of the server is the inet daemon, which then hands off to the actual server.
What ports are listened for and what processes are attached to them are defined in the server config files.
Here's a xinetd example:
To assign a port, add a "port = nnnn" line. I think by default it's using the port defined in /etc/services.
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