Payments of grants or contracts under this subchapter may be made (after necessary adjustments resulting from previously made overpayments or underpayments) in advance or by way of reimbursement, and in such installments, as the Assistant Secretary may determine. From a State’s allotment for a fiscal year which is available under section 3028 of this title the Assistant Secretary may pay to a State which does not have a State plan approved under section 3027 of this title such amounts as the Assistant Secretary deems appropriate for the purpose of assisting such State in developing a State plan.