You can do so by using a GREP.
1. Go to the GREP tab in the FInd\Change dialog in the find what field type in \d
2. In the Change Format section click on empty area and in the dialog that opens go to the "Basic Character Formats" tab and chose small caps from the Case Drop down. OK the dialog
3. Change All
You can save this query for further references.
If you add a plus sign after Javed's \d then you'll cover strings of digits in one fell swoop rather than one by one. But if you use an Opentype font that offers the figure style you want (Proportional Oldstyle?) you can put that in your paragraph style definition and let Opentype magic do the work.
David, what do you mean by "strings of digits"?
123, 456, 78, etc. are strings of digits. The plus sign is GREP for "One or more times" so it will report one search for each of those three strings when you use \d+, while \d will fix them digit by digit and report 8. But as I say, if the style of figures you want is available in an Opentype font then you can invoke it as part of a paragraph style and those figures will appear automatically.