He was a democratic socialist, yes. In a 1966 speech, he said:

There must be better distribution of wealth and maybe America must move toward a democratic socialism. Call it what you may, call it democracy, or call it democratic socialism, but there must be a better distribution of wealth within this country for all of God's children.

He downplayed his democratic socialism for much of his career due to the Cold War climate of the time. Nevertheless, he did reject actual communism, partially on religious grounds (him being a Christian preacher and all).