Just as Bloomberg promises to turn BusinessWeek into a “true” weekly with more editorial, competitor Fortune is moving even further away from the idea: the magazine is reducing frequency to 18 issues in 2010, down from 25 this year, according to WSJ. It sounds like the overture for Time Inc.‘s traditional Q4 layoffs and budget cutting. The Journal cites unidentified sources who predict a batch of cuts similar to last year’s 6 percent solution.

Prompted by the decline in ad dollars—and the 35 percent drop in ad pages, the changes coming for Fortune include a deeper focus on fewer topics and less clutter. The website will be upgraded; earlier this year, the magazine launched Brainstorm Tech . I wouldn’t be surprised to see that approach repeated as they try to highlight topics.

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