In the address Lefkowitz also criticised China and South Korea, the two countries with the most leverage over the North, for not pressuring Pyongyang enough.
He said their unwillingness to apply "significant pressure" on Pyongyang has turned recent talks into a bilateral negotiation between the US and North Korea.
In unusually sharp words, Lefkowitz also accused the North of not keeping its word saying it was not behaving as if it was "willing to come in from the cold".
Calling North Korea a "serial proliferator", he said Pyongyang used its nuclear arms to "extort" foreign aid amd questioned the administration's current approach.
"The six-party talks have not involved human rights. However, there is a valid question of whether this continues to make sense."
He said the new concept would feature human rights as a permanent part of the engagement policy and as a prerequisite for restoring diplomatic relations.
North Korea agreed in February last year to a Chinese-brokered deal under which it would declare and disable all its nuclear programmes in return for aid and other concessions.
However, at the end of the year it missed a key deadline to provide a full declaration of all its nuclear activities.
The delay is thought to centre on a dispute over what the US alleges is a separate secret uranium enrichment programme that the North has not acknowledged.