Dear Miss Snark
I was recently at a conference and was lucky enough to have an editor invite me to send her the first three chapters of my novel. I'm still revising, so I haven't began my agent search yet, but suppose I do send it to this editor who passes. Then I get an agent. Do I need to inform my agent that it was already submitted to one house? Would it be best to get an agent first ( thinking positively , of course) and then informing them that this one editor has requested to see it?
Send the pages the editor requested. If s/he says no, you'll mention that when you secure an agent (NOT in your query letter).
Don't dawdle around looking for an agent when an editor has asked for pages. It's a whole lot easier to find an agent when an editor has made you an offer. (It's not a slam dunk I know, I said 'easier' not 'guaranteed').