Is a 1999 Ford Explorer xlt rwd when 4x4 is not engaged?

1999 Ford Explorers equipped with V6 engines and 4X4 have a dash mounted selector dial for the 4X4 system . The normal operating position is in 4X4 auto. This position is rear wheel drive , but if the back wheels start to slip , some of power is transferred to the front wheels to provide assistance.