Try this:
(defun c:test ()
(if (= rad1 nil)
(progn
(setq rad1 (getreal "\n Enter Fillet Radius: "))
(setvar "filletrad" rad1)
)
)
(command "._pline")
(while (= 1 (logand 1 (getvar "CMDACTIVE"))) (command pause))
(command "._fillet" "_P" (entlast)
)
(princ)
)
You should only need to enter the radius once for each session.