The lexical function f$environment has the ability to return the current command procedure that is executing. I need to do that from a program, but I haven't been able to find the corresponding RTL routine. Any ideas?

There is no standard user available way to do
it directly, this info is in DCL-space, and needs CMEXEC privilege to access (and linking with /SYSEXE).
An example of such a program from Tom Wade posted on comp.os.vms is on my server:
http://wwwvms.mppmu.mpg.de/vmssig/src/mar/GET-COMMAND-PROC.MAR

For normal user access, I suggest to define a global symbol inside the DCL procedure, which then can be translated inside the program (by means of LIB$GET_SYMBOL or getenv()).