If 1099-int. (recd after refund) Box 1 & Box 2 have $ amts., & Box 4 "Federal Income Tax Withheld" is blank (live in NH), do I need to amend Federal return?

You do need to prepare an amended return to add the income reported in box 1 to your return. If you owe additional tax after you prepare the amended return, you should submit it. You should wait until you receive your refund if applicable before you amend the return.