rsource, terminator(END_OF_R) rpath(R_pathname)
library(foreign);
rprecar<-read.spss("precar.sav", convert.f=TRUE);
rprecar
attributes(rprecar);
write.csv(rprecar,"rprecar.csv", na = ".");
q();
END_OF_RIt may be tricky to find your R_pathname. I didn't bother looking up what it is for now - probably the path to the executable (which sucks, because on every computer it will be different). In the example the conversion goes to csv, and there's the missing values ("na") option. The foreign package actually also allows old Stata 9 files, which is just fine and will preserve most labels, variable names, and missing values.
Here's the info for -foreign-:
https://cran.r-project.org/web/packages/foreign/foreign.pdf