Atheism is associated with a materialistic doctrine that knows nothing higher than this world.
The Buddha has condemned godlessness by which He meant the denial of worship and renunciation, the denial of moral and social obligations, and the denial of a religious life. He recognized most emphatically the existence of moral and spiritual values. He acclaimed the supremacy of the moral law. Only in one sense can Buddhism be described as atheistic, namely, in so far as it denies the existence of an eternal omnipotent God or God-head who is the creator and ordainer of the world. The word ‘atheism’, however, frequently carries a number of disparaging overtones or implications which are in no way applicable to the Buddha’s Teaching.
Those who use the word ‘atheism’, often associate it with a materialistic doctrine that knows nothing higher than this world of the senses and the slight happiness it can bestow. Buddhism advocate nothing of that sort.
There is no justification for branding Buddhists as atheists, nihilists, pagans, heathens or communists just because they do not believe in a Creator God.
The Buddhist concept of God is different from that of other religions. Differences in belief do not justify name-calling and slanderous words.
Buddhism agrees with other religions that true and lasting happiness cannot be found in this material world. The Buddha adds that true and lasting happiness cannot be found on the higher or supramundane plane of existence to which the name of heavenly or divine world is given. While the spiritual values advocated by Buddhism are orientated to a state transcending the world with the attainment of Nibbana, they do not make a separation between the ‘beyond’ and the ‘here and now’. They have firm roots in the world itself, for they aim at the highest realization in this present existence.
Source : www.sinc.sunysb.edu