In answer to the resolution of the Senate of the 3d instant, I communicate herewith estimates prepared by the War and Navy Departments of the probable expenses of conducting the existing war with Mexico during the remainder of the present and the whole of the next fiscal year. I communicate also a report of the Secretary of the Treasury, based upon these estimates, containing recommendations of measures for raising the additional means required. It is probable that the actual expenses incurred during the period specified may fall considerably below the estimates submitted, which are for a larger number of troops than have yet been called to the field. As a precautionary measure, however, against any possible deficiency, the estimates have been made at the largest amount which any state of the service may require. It will be perceived from the report of the Secretary of the Treasury that a considerable portion of the additional amount required may be raised by a modification of the rates of duty imposed by the existing tariff laws. The high duties at present levied on many articles totally exclude them from importation, whilst the quantity and amount of others which are imported are greatly diminished. By reducing these duties to a revenue standard, it is not doubted that a large amount of the articles on which they are imposed would be imported, and a corresponding amount of revenue be received at the Treasury from this source. By imposing revenue duties on many articles now permitted to be imported free of duty, and by regulating the rates within the revenue standard upon others, a large additional revenue will be collected. Independently of the high considerations which induced me in my annual message to recommend a modification and reduction of the rates of duty imposed by the act of 1842 as being not only proper in reference to a state of peace, but just to all the great interests of the country, the necessity of such modification and reduction as a war measure must now be manifest. The country requires additional revenue for the prosecution of the war. It may be obtained to a great extent by reducing the prohibitory and highly protective duties imposed by the existing laws to revenue rates, by imposing revenue duties on the free list, and by modifying the rates of duty on other articles. The modifications recommended by the Secretary of the Treasury in his annual report in December last were adapted to a state of peace, and the additional duties now suggested by him are with a view strictly to raise revenue as a war measure. At the conclusion of the war these duties may and should be abolished and reduced to lower rates. It is not apprehended that the existing war with Mexico will materially affect our trade and commerce with the rest of the world. On the contrary, the reductions proposed would increase that trade and augment the revenue derived from it.