Irrigation districts which embrace lands for which works have been constructed by the United States and water right applications or contracts made and accepted under public notice issued by the secretary of the interior, may provide by contract with the United States for the release of mortgages or liens given or reserved to the United States upon district lands and for the assumption by the district as principal or guarantor of the indebtedness to the United States on account of district land and in that event shall apportion the benefits of such contract and release to the lands benefited thereby in the same manner provided by statute for the apportionment of the benefits of a bond issue or other contract: provided, such contract with the United States be authorized by the electors of the district in like manner and by the same majority as required to authorize a bond issue or contract with the United States for construction of works.