She was shown a string of emails addressed to her from journalists while she was editor at the Sun, many asking her to approve payments, at London's Old Bailey yesterday.
Some did give the source but may have involved officials such as serving police or Army personnel, the jury heard.
Mrs Brooks, 45, of Oxfordshire, said: "I have never knowingly sanctioned the payment of a police officer for information in the line of his duties."
She added: "You would not pay a public official unless it was in the public interest."
She said she approved one reporter's request in less than a minute for cash for his, "but never considered whether it was a public official", the court heard.
She insisted that she "assumed" it was not.
Mrs Brooks was asked if she ever considered that the number one contact the Sun was paying was "pretty well placed".
She replied: "Probably not."
She cited the seniority and experience of the journalist concerned, to which Mr Edis retorted: "So you decided not to do your job because you thought he was doing his, is that what it comes to?" She denied this.
All defendents in the trial deny all charges against them.
The trial continues.