(a) Every contract subject to this Act which is indefinite in amount is required to contain the clauses prescribed in § 4.6 for contracts in excess of $2,500, unless the contracting officer has definite knowledge in advance that the contract will not exceed $2,500 in any event.

(b) Where contracts or agreements between a Government agency and prospective purveyors of services are negotiated which provide terms and conditions under which services will be furnished through the use of service employees in response to individual purchase orders or calls, if any, which may be issued by the agency during the life of the agreement, these agreements would ordinarily constitute contracts within the intendment of the Act under principles judicially established in United Biscuit Co. v. Wirtz, 17 WH Cases 146 (C.A.D.C.), a case arising under the Walsh-Healey Public Contracts Act. Such a contract, which may be in the nature of a bilateral option contract or basic ordering agreement and not obligate the Government to order any services or the contractor to furnish any, nevertheless governs any procurement of services that may be made through purchase orders or calls issued under its terms. Since the amount of the contract is indefinite, it is subject to the rule stated in paragraph (a) of this section. The amount of the contract is not determined by the amount of any individual call or purchase order.