The police provided for in section 167 of this title shall have the power, within the Library of Congress buildings and grounds and adjacent streets, to enforce and make arrests for violations of any provision of sections 167a to 167e of this title, of any regulation prescribed under section 167f of this title, or of any law of the United States, any law of the District of Columbia, or of any State, or any regulation promulgated pursuant thereto: Provided, That the Metropolitan Police force of the District of Columbia are authorized to make arrests within the Library of Congress buildings and grounds for any violations of any such laws or regulations, but such authority shall not be construed as authorizing the Metropolitan Police force, except with the consent or upon the request of the Librarian of Congress or his assistants, to enter the Library of Congress buildings to make arrests in response to complaints or to serve warrants or to patrol the Library of Congress buildings or grounds.