While the
argument rages on the internets I have to say that from my point of view he was not.
First of all it should be noted that President Ford's first impulse in 1974 was to increase taxes. It was only after a Republican debacle at the polls in the midterm elections (though President Nixon's activities bear much of the blame for that) that President Ford decided to listen to other voices. (As a historical aside it is interesting to note that Donald Rumsfeld and Dick Cheney played a role in this as the President's Chief of Staff and Deputy Chief of Staff. Cheney was also Arthur Laffer's classmate at Yale.)
The tax cuts cited by people claiming he was were largely demand-side tax cuts. That is, they were targeted towards people who would immediately spend the money; people on the lower end of the income scale. There were no reductions in marginal tax rates and thus no incentives to invest or earn more money to reap the benefits of future lower tax rates. In addition the scope of the cuts was small (limited to lower-incomes) and limited in duration (though Ford could hardly control what economic policies Carter would follow).
It is possible that if he had been reelected in 1976 that he would have become a Supply-Sider, as his
1976 State of the Union speech detailed a number of supply side policies including tax rate cuts.
Voters, however, chose a different track for the remainder of the 1970s before deciding that Supply Side was worth another look in 1980.