The move will take place when current chairman Paul Finch steps aside in the summer to concentrate on his role as design adviser to the Olympic Delivery Authority.
It is understood that the Design Museum's Deyan Sudjic will be drafted in to become a CABE commissioner when the reshuffle takes place in August.
Sudjic has been shadowing Finch for some time and it was rumoured that the architecture critic would be taking over as chairman.
However, a source close to CABE has placed Long as the firm favourite to take the post.
Long already acts as a commissioner for CABE and is a vice-chairman along with Louisa Hutton, Ken Shuttleworth and Robin Nicholson.
A CABE spokesman said: 'Paul Finch will be stepping down in August and we can confirm Deyan Sudjic will be taking over as a commissioner.
'However, no decision has yet been made as to who will take over from Paul Finch in his capacity as chairman of the design review committee.'