Sol had a defense perimeter at Jupiter and Mars by BoBW, I'd assume that Earth would have some means of protection as well--given its significance to the UFP.
The Breen could've been cloaked until they reached orbit, dropped their cloaks and attacked. Very few Breen ships were said to have survived, it wasn't said just how they'd been destroyed, so orbital or surface-to-orbit weaponry could've been the cause.
Commander Austin Harris, First Officer, Deep Space Nine (by FltCpt. Bossco)
8.01 - Darkest Before Dawn
(Chapter 8 added, 12/09/2015)