I'm laying out a book. Images are in color. I want the book to be in black and white, with images using halftone patterns. Are there any export options to obtain this output?
There are no options for that in InDesign, except (in newer InDesign's) wholesale Export to Grayscale PDF. That may not even be necessary if you instruct your print shop to print your document in gray -- although you have more control over the to-gray conversion if you do this yourself beforehand.
You cannot physically save the common halftone parameters in your PDF¹ -- halftone frequency, angle, and dot/line pattern -- because it is best to leave it at the printer's discretion. Suppose you save a high screen frequency in your PDF, meant for offset printing: 120 lines per inch. Printing the file on a laser printer would result in an ugly print-out because a laser printer cannot reliably reproduce such a frequency (higher frequency equals more, and thus smaller, dots; there is a bottom limit on how small the halftone dots can be before they merge with physically printed dots). On the other hand, if this file is to be printed on a high resolution output device such as an art quality offset press, then you'd get a lesser result than what would be possible.
Leaving it to the output device also pretty much guarantees that all your images will be converted to halftones in the exact same way.
You can ask your print shop about their specific output process, as in general printers (the people) are happy to share there experience with you. (And if they are not, you could always find another who are.)
You can use InDesign's own Export To Gray option right away, or use Photoshop to convert all, or only some critical, images to grayscale -- definitely not to "Bitmap"! Photoshop's "Halftone Bitmap" is meant only and exclusively for special design effects--definitely not to produce "print ready" halftones!
Using Photoshop means you have total control over contrast and brightness, and with the "Black and White" filter you can even enhance or surpress individual color ranges. (Remember, though, that this a filter and so it still leaves the original file in RGB mode. You may want to convert your images to grayscale after using it.)
¹ The PDF specification does allow it, but InDesign doesn't have an interface to do so.