This is not correct. First, in straight and level flight, the aircraft produces as much lift as is needed to counter its own weight, so this stays constant regardless of the other parameters. If you meant the wing area is decreased due to the sweep, that would mean the lift stays the same but the lift COEFFICIENT increases, which would cause an increase in induced drag, while the smaller wing area would mean a decrease in skin friction and profile drag.That's why Tomcats swept their wings backwards at high speeds... To reduce lift and ie reduce drag - Same with the Bones.
However, those two drag changes are very small compared to the reduction in wave drag you get at transonic and supersonic speeds due to wing sweep regardless of any change in wing area. The reason for sweeping the wing at high speed is therefore so that (a) the swept leading edges reduce the wave drag and (b) the area distribution along the length of the aircraft more closely conform to the area rule, which also decreases wave drag. The reduction in drag in this case is not due to any change in lift.
At low speed (below the transonic regime), the wave drag is insignificant while the other drag components are more important. In this case, a high aspect ratio helps to decrease induced drag, so at those speeds long straight wings are beneficial again and a variable sweep aircraft will fly with its wings in the unswept position. Depending on the wing geometry, there may also be a small increase in wing area in the unswept configuration which will decrease the stall speed of the aircraft.