OPERATIONS IN KENTUCKY AND TENNESSEE.

HEADQUARTERS WESTERN DEPARTMENT, Bowling Green, November 8, 1861.

HonorableJ. P. BENJAMIN, Secretary of War:

SIR: The great superiority of the enemy's force had enabled him to place a heavy column, estimated at 20,000 men, in front of me, and to concentrate auxiliary forces of Kentuckians, supported by Federal troops, on my right and left, threatening flank movements. One of these movements has for its object Nashville, Tenn., which is one of our principal depots, where large supplies of subsistence for the army East and West are accumulated, and valuable manufactories of arms, powder, clothing, &c., are established and in successful operation. The object of the other movement is the breaking up of the Memphis and Ohio Railroad, and the occupation of Clarksville, Tenn., which, if effected, turns the right of the column under General Polk's command.

The effectiveness of the force here is considerably dimished by sickness (in most cases measles), and the same cause has left but a small portion of General Tilghman's command at Hopkinsville, Ky., fit for duty.

These considerations have induced me to draw 5,000 men from General Polk's command to cover the defenses of Clarksville. The Cumberland River defenses will also be thus provided for, besides enabling me to drive back the forces of the enemy concentrating at Hartford, north of Green River, designed, I think, to operate against Clarksville and Russellville, both of which are on the Memphis and Ohio Railroad.

Three regiments will garrison the fort at Columbus. After deducting them and the force ordered to Clarsville, 10,000 or 11,000 effective men will be left under General Polk's command; a sufficient force for the defense of his front for the present, but much less than I would suggest for the contingencies of the future.

The country between Columbus and the Tennessee River is generally covered by a heavy forest with undergrowth and is intersected by numerous roads. It can be defended by a force inferior to the invading force. I am not apprised that the force of the enemy which may be put in motion in his front is superior to that of General Polk.

The iron-clad gunboats of the enemy have appeared in the cumberland River, but were prevented from ascending higher than near Eddyville by obstructions lately placed there by order of General Polk. Boats loaded with stones and sunk on the shoals have also been placed in the river at Line Port.

Twelve miles above Line Port is the site of Fort Donelson. By this time it is in a state of defense, having, besides other guns of less caliber, four 32-pounders and a sufficient garrison. I have also sent to that point four other 32-pounder guns.

Fort Herny is located on the Tennessee River, about 12 miles from Fort Donelson. It is a strong work, and sufficiently garrisoned by an excellent regiment. There is a small supporting force at each of these forts, consisting at Fort Donelson of one regiment of cavalry and at Fort Henry of one regiment of infantry.

I find it extremely difficult to acquire reliable intelligence of the movements of the enemy, except that which the activity of our scouts enables them to furnish, and would be glad to have $5,000 deposited in Nashville bank to my credit for secret service.

I beg leave to ask that the staff of the disbursing department, particularly the commissary department, may be supplied at the earliest practicable moment with money.