In R, is it possible to save the current workspace without quitting?

You can use save.image() at any time to save all environment data into an .RData file:

save.image(file='yoursession.RData')

To load this data later you can use:

load('yoursession.RData')

Apart from save.image() function, that lets you save the entire workspace, you can also check the save() function.

save() function lets you save individual objects in the workspace.

 save(ObjectToBeSaved, file = "FileName.RData")