HEADQUARTERS ARMY OF THE POTOMAC, September 28, 1862.

Brigadier General LORENZO THOMAS,
Adjutant-General, U. S. Army:

GENERAL: The reduced condition of the old regiments,and the futinty of dependence upon the recruiting service for the replenishing of their ranks, points to the necessity of earnest endeavor to collect all the absent officers and men belonging to these organizations. I am aware that this subject has already occupied the attention of the War Department; but I am now more especially alluding to the class of absentees employed on extra duty in the hospital and other staff departments of the Army, who are the most valuable of the absentees (for many absent men are runaways), and who can be sent to their regiments now without difficulty, inasmuch as their places can be readily supplied from new troops. I am now getting together stragglers and convalescents from hospitals, and if I could get extra-duty men also, a very considerable addition would be made the the diminished ranks of the old regiments.

In order to carry this into effect, I respectfully suggest that an order be issued fixing a time, say the 15th of October, when all hospital attendants and other extra-duty men shall be relieved and sent to the convalescent camp at Alexandria, in depot, from which they can be drawn and sent to their regiments as soon as a sufficient number have accumulated to justify the sending for them. The order should prohibit any officer retaining a soldier of the old regiments without the consent of the War Department or of the commander of the army or department to which the soldier belongs.

I suggest that every hospital and staff office be inspected within the month of October, by, if necessary, scores of officers detailed for the purpose, to ferret out the old soldiers hidden away therein. Such an inspection would produce more fruit in one week than the recruiting service can the three months.

And, finally, I suggest to the War Department the employment of the deputy provost-marshall throughout the North, more particularly in the arrest of deserters. Convalescent soldiers leave hospitals, and have done so for the past year, and return home habitually. It is the experience of every army commander that not more than a tenth of the soldiers who are left behind sick every rejoin. A regiment here, which has been employed pretty much during the whole year as depot guard, has had in the course of the year some 500 sick sent to hospitals in the rear. Of these it has received back some 15 or 20. The stragglers, too, are numerous in every division of the army; many of these desert. The States of the North are flooded with deserters, absentees, &c. One corps of this army has 13,000 and odd men present and 15,000 and odd absent; of this 15,000; 8,000 probably are at work at home, deserters. They can be secured and returned, and I beg that the fullest exercise of the power of the Government may be devoted, if necessary, to the accomplishment of this end. It will have the happiest result in swelling the ranks of the old regiments, and in preventing their future reduction.

I am, general, very respectfully, your obedient servant,

GEO. B. McCLELLAN,

Major-General, Commanding.

P. S.-Since writing the above, General Orders, No. 140, of September 24, 1862, has come to my notice. The Department has, therefore, anticipated my suggestions with regard to the employment of deputy provost-marshals.