find your_folder -type d -exec chmod your_permissions {} \;
If you only want to change the permissions for files in your_folder itself and not in its subfolders you can add -maxdepth:
find your_folder -maxdepth 1 -type d -exec chmod your_permissions {} \;
Example: find my_folder -type d -exec chmod 644 {} \;
Or, if there are many objects to process:
chmod 755 $(find /path/to/base/dir -type d)
chmod 644 $(find /path/to/base/dir -type f)