All boards, commissions and heads of departments of the State Government may invest moneys or funds in their possession in the following securities:
No investment of such funds shall be made where the total debt of any such municipality, including the school debt, shall exceed thirty per centum (30%) of the assessed valuation of all the real and personal property therein; but in ascertaining the total indebtedness, credit shall be allowed only for such moneys or property as shall be in the sinking fund.
N.J.S. § 52:14-31