Could we track Extraterrestrial Space craft right now?

How about "there aren't any"? Well, first of all, we aren't really looking for alien spacecraft, but we are looking for asteroids that could threaten Earth, and I suspect the equipment would've picked an alien spacecraft up. You can't find something that isn't there no matter how hard you look.

That said, 30000km isn't that far in space, and a 3m aperture IR telescope would be quite hefty. In practice, stealth in space might be more feasible than we assume. In COADE, each faction has huge telescopes in solar orbit for tracking ship movement, but in case such infrastructure was absent, reflective heatshields and hiding behind celestial bodies could enable, at the very least, some degree of surprise for interplanetary approaches. If you really want aliens to be a thing, just tell yourself they're making an effort to hide from us. With the currently existing infrastructure, it's not hard as long as they're not orbiting Earth (and even then, the Moon provides a convenient hiding place on its far side).

Of course, the aliens would have to come from somewhere, and that presents a problem. Interstellar objects are pretty conspicuous and generate a lot of interest from the scientific community. Interstellar drives are massive (what with basically being torchdrives) and rather hard to hide. The aliens would have had to arrive before we started to study the sky with anything more than an optical telescope, over 100 years ago. I really think the most reasonable answer is "there aren't any aliens in our solar system".

Size doesn't matter, brightness does. And any sort of interstellar drive would be ridiculously bright. And it would be bright for a long, long time, not just during acceleration (when it'd be pointed away from us, anyway), but when decelerating. To be efficient, an interstellar drive has to run hot, and because of that, the plume would glow. It would be really hard to miss during the braking phase, basically, it would look like a new, point source of light with a spectrum unlike any star in the sky. Spectrometry is a routine thing to do to such light sources, as a matter of fact, we cannot yet see the disk of any bodies located outside our solar system, so it's the only way we can find anything about what we're seeing. I guarantee you, a strong source of light appearing out of nowhere would have astronomers all over it in a short time. We can measure even very small parallaxes, so we would be able to tell that it's fairly close, too. In short, there's no way we'd miss something that conspicuous.

Now, for things that don't decelerate, well, we had that funny-shaped interstellar rock go through the solar system. But this one was detected and tracked, all right. We didn't find out much about it, and if it was an alien ship, we'd never know, but it didn't hang around for long and was rather cold, anyway. Think of it: if we were able to track an interstellar asteroid so far in advance as it crossed the solar system, what are the chances of us missing a starship that's blasting the general area with all sorts of relativistic radiation (any interstellar engine worth its salt has a relativistic exhaust plume) from its engine? There are ways of making interplanetary starships if not stealthy, then at least reasonably inconspicuous. Not so with interstellar ones.