(I) would if I could

(I) would if I could

I would like to do whatever has been asked of me, but I am unable to. Sometimes used humorously or sarcastically. A: "Isn't there anything you can do to expedite our claim?" B: "I would if I could, really, but my hands are tied." A: "Hey, would you please clean out the gutters like I asked?" B: "Ah, sorry, would if I could, but I really must be going."
See also: could, if
Farlex Dictionary of Idioms.

(I) would if I could(, but I can't).

I simply can't do it. Jane: Can't you fix this yourself ? John: I would if I could, but I can't. Bob: Can you go to the dance? Hardly anyone is going. Alice: Would if I could.
See also: could, if
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • as far as the eye can see
  • as far as the eye can/could see
  • this just in
  • believe it or not
  • bion
  • are we having fun yet
  • Are we having fun yet?
  • AWHFY
  • aforethought
  • riddle me this/that