refering to variable names in lm where the variable name is in another variable

I am trying to refer to a variable name in a lm regression where the variable name is in another variable, but it does seem to work.  Here is an example:

y<-rnorm(10)
dat<-data.frame(x1=rnorm(10),x2=rnorm(10),x3=rnorm(10))
nam<-c('x1','x2','x3')
library(gtools)
com<-combinations(3,2,1:3)
mod<-lm(y~nam[com[1,1]],data=dat)

#error in model frame....:variable lengths differ().

I also get the error if i just refer to variable x1 as nam[1] in the lm. any suggestions.  I am trying to set up a for loop that will perform an all subsets regression and calculate the AIC for each.

Dan