My friend says he heard someone on the radio saying that there were
more white slaves than black slaves in early America.  I'm almost
certain that can't be right, but I haven't been able to locate any
demographic information related to the race of American slaves.  What
was the racial break down of American slaves?

If indentured servitude counts as "slavery," then the statement your
friend heard on the radio is true.

"One hundred and sixty years before the Revolution, slavery existed in
North America. The first slaves were Native American. The first
African slaves arrived in 1619, BUT the primary slaves of that age
were indentured servants from Scotland, and Ireland. Their servitude
was to last seven years, then they would be free, yet about half never
lived seven years."

http://72.14.207.104/search?q=cache:NYnQRKUIf8QJ:www.yorknewstimes.com/stories/112700/edi_1127000002.shtml

"One half to two thirds of all immigrants to Colonial America arrived
as indentured servants. At times, as many as 75% of the population of
some colonies were under terms of indenture. Even on the frontier,
according to the 1790 U.S. Census, 6% of the Kentucky population was
indentured...

The importation of white servants under contracts known as indentures
proved more profitable as a short-term labor source than enslaving
Indians or using free labor. Eventually, the final attempt to ease
labor shortages was enslavement of Africans. Wherever you find
slavery, you first find indentures...

Criminals convicted of a capital crime in England could be transported
in lieu of a death sentence (for the theft of an item with a cost of
as little as one shilling). Servitude also could result from
indebtedness, where a person, their spouse or parents owed money, and
the person was sold into servitude to recover the debt. In other
cases, a parish indentured orphans in order to keep them off the poor
roles. Plus, the poor sometimes sold themselves into indenture just to
survive.

In most cases, the work of the indentured servant would be household
or agricultural unskilled labor. There was also a great demand for
skilled craftsmen. If an indentured servant had a skill that was in
demand, like weaving, smithing or carpentry, the change of negotiating
a shorter contract was quite good.

In theory, the person is only selling his or her labor. In practice,
however, indentured servants were basically slaves and the courts
enforced the laws that made it so."

http://www.geocities.com/nai_cilh/servitude.html