Although LDS Church President Brigham Young, as well as some apostles opined such things, the answer to my question is NO. Such an idea was never unanimously accepted as doctrine by the general councils of the Church as is required (see Doctrine and Covenants section 107).
I am aware of only one statement ever expressed in an LDS General conference to the effect that blacks were less valiant in pre-mortality (by Apostle George F Richards). Since then, several statements have been made to rebut such an opinion.
Was such a thing taught over the pulpit in LDS congregations? Besides the one time in LDS General Conference that I am aware of, I was a participant in an LDS Sunday School class at about the age of 12 where I was taught this concept. I distinctly remember
- Which room of our church meetinghouse I was when I was taught this
- Who taught it to me
- That they used the metaphor of a running track to indicate how black people were behind white people in their pre-mortal valiance
- AND how bizarre I thought this teaching was
Was such a thing believed by LDS Church members. Unfortunately, yes. Probably along these lines, I was in a fireside where Thurl Bailey spoke of how traumatized his white girlfriends parents were when they first met him and found out that he was black. Eventually, however, Thurl's girlfriend's parents got over their prejudices, and they accepted him. Thurl's then girlfriend is now Thurl's wife.
Here are some interesting excerpts from an interview with Apostle Legrande Richards shortly after the 1978 revelation granting black men the LDS priesthood:
"Some time ago, the Brethren decided that we should never say that [blacks were less valiant in pre-mortality]. We don't know just what the reason was [for blacks not holding the priesthood before 1978]. We don't want to get that as a doctrine. The Lord has never indicated that black skin came because of being less faithful."