AT the State Department Building in Washington's Foggy Bottom, office windows glow far into the night. Presidential address-drafters (Contingency Division) are apparently preparing for every eventuality. One draft of a possible Johnson TV address to the nation, found scribbled on the flyleaf of an abandoned copy of Barbara Ward's The Rich Nations and the Poor Nations, reportedly reads as follows:

"My fellow Americans:

"We have sensed concern from some quarters about last month's loss of Saigon to the Communists. In certain instances, this concern approaches that first felt for the loss of the American embassy for a few hours back in February.

"Now as then, there is no cause for alarm. Your government has known for several months that the Communists planned a massive spring offensive aimed not only at Saigon, but at all of Vietnam.

"The stated purposes of the Communist uprisings have failed. Communist leaders counted on widespread support among the populace for their effort. Populace or support--they found little or none.

"The loss of a national capital should not prove disheartening to the Saigon government. We Americans can point with pride to our own history, to 1814, when the British captured and burned this very city of Washington from which I am speaking to you tonight. Tonight the United States stands great, while the British are known mostly for funny movies and a bum pound.

"We can point with pride to World War II, when the great capital city of Paris, France, fell to the Nazis of Germany. But I ask you--who won the war? Certainly not the Nazis.

"And finally we can point with pride to Korea, which, like Vietnam, is in Asia. Communists captured the capital of the unfortunate Koreans in 1950 but, of course, we Americans were only marking time. And tonight's latest diplomatic cables show that the capital of South Korea remains free of Communist control.

"In Vietnam, the United States still retains its strong position in the provincial capitals of Mau Can, Can Tho and Tho Whut. Even as I speak to you tonight, valiant American men are battling to regain the green beret encampment near Cho Lon.

"YOUR President--and we want to keep in mind that he's the only one you've got--is happy to report that the Communists failed to capture the American embassy in Saigon. Armed with the knowledge gained from the Pueblo maneuver, our officials managed to blow up the embassy before it could fall into enemy hands. The leg injuries sustained by Ambassador Ellsworth Bunker are not believed to be serious.

"We have asked the Soviet Union to put pressure on the Hanoi government for the release of Ambassador Bunker, as well as Mrs. Charles Percy. Until such time as their release is effected, I can only reiterate the stand taken by Mr. Rusk: 'My strong advice to Hanoi is to cool it. There have been enough of these incidents.'

"We want the world to know we stand foursquare behind our Secretary of State in this matter. But there are no easy solutions, and therefore we do not think Sen. Wallace Bennett's advice to 'send an armored division roaring into Saigon, throw a tow rope around Ambassador Bunker and Mrs. Percy, and haul them out of there' is particularly helpful.

"We also think the American voters will have the good sense to recognize Mr. Nixon's description of the loss of Saigon as a 'tactical blunder' as so much election year blarney.

"We are also happy to report that General Westmoreland has escaped Saigon safely to a windowless command center on Formosa where, incidentally, Chiang Kai-shek has offered 33,000 Nationalist Chinese troops for use in Vietnam.

"We dont want to prophesy on what is going to happen in Vietnam or why. We feel reasonably sure of our strength. We will continue to fight until there is some better sign than these last weeks have provided of Hanoi's willingness to concede defeat.

"We are of course taking such precautionary steps as we may think the military situation calls for. We have ordered the aircraft carrier Enterprise to the South China Sea.

"I see no reason to increase American force levels in Vietnam beyond the 525,000 men now scheduled to serve there. I would not want to foreclose any action on a matter like this, however. Anything can happen."