United and American airlines flights going anywhere in the country were booked solid yesterday, the last day of the great airline half-price giveaway.

What was being given away were half-price coupons entitling the holder to a 50 percent discount on any domestic United or American flight between July 1 and Dec. 15. Coupon-shoppers jammed airports nationwide yesterday, waiting for cancellations on any flight going anywhere for a last chance to get a half-fare bargain.

At Washington National airport, there wasn't a single cancellation on any United flight, to the dismay of last-minute bargain-hunters who jammed ticket counters and waiting lists, hoping to fly standby.

"The response to the coupons has just been phenomenal," said John Leskow, a United passenger service supervisor at National.

"With the DC 10 groundings and this other thing, I think it will be a little while before we can determine what effect this will have on business in the long-run," said an American spokesman in New York.

United originated the half-fare coupon giveaway at the end of May as a sales gimmick to recover business lost during a lengthy strike. Within days, American followed suit and started giving away half-fare coupons to its passengers.

Cindy Horton, an American reservations clerk in Chicago, summed up the last three weeks of coupon mania: "Everybody's really tired of this. The call-waiting light has never gone off the whole week."