Mr Hitchens said it was necessary to "state a clear and conservative alternative" to Mr Portillo's "washy moderation" and to "the strange, bland new creed" that he appeared to have adopted.
The outspoken attack by Mr Hitchens, known for his strident opinions in The Express, follows the former defence secretary's decision to admit he had homosexual experiences at university, before public life.
Mr Hitchens wrote in The Spectator: "Like so many of his generation, I would guess he [Mr Portillo] does not much like this country as it is now or recently was, and wants to turn it into somewhere and something else. I think homosexual acts are wrong. However, having done many seriously wrong things myself and fearing I will do many more this side of the grave, I cannot believe that this is a political issue or even my business."
Mr Hitchens said that when Mr Portillo was a schoolboy he had a picture of "that dreadful, unprincipled trimmer and phoney" Harold Wilson taped to his locker. He added: "Teenage enthusiasts for washy moderation have a nasty habit of growing up into adult enthusiasts for washy moderation."
But both men will have to fight off Rupert Allason, the former MP and spybook writer Nigel West, who also wants to contest the safe Tory seat. A close ally said Mr Allason was a "strong local candidate who has lived in the constituency since he was one year old". The left wing of the party plans to put forward a "stop Michael" candidate because of his arch Euroscepticism, although insiders say they have yet to find someone high-profile enough for the royal borough.
The constituency's Conservative Association meets today to decide a selection process timetable. Central Office has not named a date for the by-election, caused by the death of Alan Clark.
A friend of Mr Portillo, former MP for Enfield Southgate, said he was determined to avoid high-profile appearances at the party conference in Blackpool to show loyalty to William Hague.The party leadership is privately concerned Mr Portillo's possible return to Westminster will overshadow the conference and take the gloss from the planned launch of several key policies.
Several Sunday newspapers are said to be planning more revelations about Mr Portillo's "gay past", with kiss-and-tell stories by former boyfriends.Reuse content