first fifteen years after the effective date of the Compact, the President (either through an appropriate department or agency of the United States or by contract with a United States firm or by a grant to the Government of the Republic of the Marshall Islands which may further contract only with a United States firm or a Republic of the Marshall Islands firm, the owners, officers and majority of the employees of which are citizens of the United States or the Republic of the Marshall Islands) shall provide technical and other assistance without reimbursement, to continue the planting and agricultural maintenance program on Enewetak