ALEXANDRIA, VA., August 28, 1862 - 1 p. m.

(Received 1.5 p. m.)

General H. W. HALLECK,

General-in-Chief:

Your dispatch to Franklin received. I have been doing all possible to hurry artillery and cavalry. The moment Franklin can be started with a reasonable amount of artillery he shall go. In the mean time see Whipple's dispatch; something must be done in that direction. Please see Barnard, and be sure that the works toward Chain Bridge are perfectly secure. I look upon these works, especially Ethan Allen and Marcy, as of the first importance. I have heard incidentally that there is no garrison in Ethan Allen, but presume it is a mistake. I have just conversed with Colonel Holabird, and think the enemy is in such force near Manassas as to make it necessary for us to move in force.

GEO. B. McCLELLAN,

Major-General, Commanding.

ALEXANDRIA, VA., August 28, 1862.

(Received 2.45 p. m.)

Major General H. W. HALLECK,

General-in-Chief:

From a full conversation with Colonel Scammon I am satisfied that the enemy is in large force between us and Pope. One of his surgeons, who was taken and released, saw Jackson, A. P. Hill, and three other generals. At about 5 p. m. yesterday the re was heavy cannonading in direction of Manassas. it is my opinion that any movement made from here must be in force, with cavalry and artillery, or we shall be beaten in detail. Can you find a squadron to go to Vienna, via Lewinsville, and ascertain whether enemy there? The right of our line of works on this side the river should be most carefully watched and pickets well out on all roads. Vedettes should extend at least to lewinsville and Prospect Hill - if possible to Meridian Hill and on the ridge thence to Dranesville. It is of vital importance to know what there is near Vienna at once. The impressions I receive from Scammon are corroborated form other sources. I don't see how McDowell can well be at Gainesville. It is of vital importance to know what there is near Vienna at once. The impressions I receive from Scammon are corroborated from other sources. I don't see how McDowell can well be at Gainesville. Have this moment received intelligence from a prisoner, captured the other night and just escaped, that he saw Jackson, Stuart, and Minke [?]; that the enemy were 30,000 strong in vicinity of Manassas and being re-enforced constantly. I suggest that you take into consideration the propriety of Pope falling back via Davis', Spiggs', and Bradley's Fords, &c., between the Occoquan and Potomac, and rejoined vie Wolf Run Shoals, Occoquan, &c., our best troops here advancing, say to-morrow morning or to-night, if ready, so far as Fairfax, Brimstone Hill, and Wolf Run Shoals, to cover the movement. I do not think it now worth while to attempt to preserve the railway. The great object is to collect the whole army in Washington, ready to defend the works and act upon the flank of any force crossing the Upper Potomac. If Pope makes this movement, steps must be taken at once to build pontoon bridges over the Occoquan.

GEO. B. McCLELLAN,

Major-General.