Sec. 1. All repair or construction of any work or public improvement in the chartered cities, except parks, boulevards,streets or alleys involving an estimated cost of three thousand pesos or more shall be awarded to the lowest responsible bidder after public advertisement in the Official Gazette for not less than ten days, by the mayor upon the recommendation of the city engineer: Provided, however, That the city engineer may, with the Approval of the President of the Philippines upon the recommendation of the Secretary of Public Works and Communications, execute by administration any such public work costing-three thousand pesos or more.
In the case of public works involving an expenditure of less than three thousand pesos, it shall be discretionary with the city engineer either to proceed with the work himself or to let the contract to the lowest bidder after such publication and notice as¦shall :be deemed appropriate or as may:be, by regulation, prescribed.