Charles B. Rangel, the venerable but embattled congressman from Harlem, will announce on Thursday that he is running for a 23rd term, according to a colleague in the New York House delegation. Representative Rangel — who in an unusually introspective email to supporters over the weekend prompted speculation that he might retire — told the colleague, Representative Gregory W. Meeks, this week that “I haven’t announced yet, but I want folks to know that I am going to do it.” “He is full of energy,” said Mr. Meeks, a fellow Democrat.