The short answer is no, because "theism is false" is actually further than most atheists are willing to go.
Even Richard Dawkins would not unequivocally say there are no gods, which must be true in order to conclude that theism is false. The chapter of The God Delusion directly concerned with God's existence is titled, "Why there *almost* certainly is no God".
Would you say that because Dawkins felt he needed the "almost", Richard Dawkins is not an atheist? Of course not. Atheism is not a stone cold denial, it's not a positive belief that there are no gods (that's "strong atheism"). It's a lack of belief in any god or equivalent and the associated conclusion that there probably aren't any. To invite atheists to argue that theism is definitely false is like inviting an astronomer to argue that aliens are impossible.
Here it is from the standpoint of statistics. It's impossible to disprove a null hypothesis; you can only find sufficient evidence to reject it and accept an alternate hypothesis. The absence of any gods is the null hypothesis, because it requires no evidence to even suggest.
This is proven by the existence of "implicit atheists", those few with no exposure to religion and no self-taught religious beliefs. Many young children and some remote tribespeople are examples. Atheism is the default position for a human being, at least to begin with. Any god is therefore an alternate hypothesis which you may accept on the basis of whatever you regard as evidence. You can never deny the possibility outright. I don't try.
Moving from the disputed truth of theism to the pros and cons of professed theism: With the possibility of a god intact in my mind, this atheist is ostensibly at risk of paying dearly in hell while believers are rewarded. This is only likely to be the case if there is only one possible god. There are 20,000 or so invented gods and an infinite number of other possible gods. Whatever the probability of SOME god existing, the probability of a particular god is one in infinity, or near to zero as darn it. Live as though only your god or gods exist and, infinity to one, you're backing the wrong horse. The vast majority of invented gods are very unforgiving of that. Better to approach the worst-case scenario of a foreign god with no other gods in hand, I say. Besides, wouldn't any god see through a fake self-serving belief professed only to escape punishment?
As you can see, theism invites criticism even when you admit it is not definitely false.
The following is an attempt to reason against theism as strongly as an honest atheist should dare.
Premise 1: There is no apparent empirical evidence for the existence of any god or equivalent supernatural being.
(Break this premise if you like by presenting some. The value and definition of "apparent empirical evidence" will need hammering out first of course, and I won't do that here.)
Premise 2: For the truth of theism to be at all likely, some empirical evidence for the existence of a god or equivalent supernatural being would need to be apparent.
(You'd need a very good reason why some other type of evidence is acceptable, or even evidence at all.)
Conclusion: Theism is likely false.
I invite readers to try writing their own step-by-step logical arguments in a similar vein. Have fun.
(As a sidenote, Penn Jillette once wrote an article called "There is no God." You might like it. - Brian Sapient)
Thankyou for wording the question so well.
Let's split this hypothetical higher power into its two possible roles: creator, and intervenor.
A being which directly created the universe to a design would have to be more complex than the whole thing put together, and therefore be the most complex and unlikely thing in existence. Furthermore it would itself need an even more complex creator, and so on ad absurdum. If you assert that the creator has existed forever and needs no creator-creator, why can't the (less complex) universe be eternal and need no creator in the first place? Whatever constraints you put on the universe to necessitate a creator, you immediately have to break to allow a creator. It's just not a good explanation by any standard at all.
Now consider an interventionist entity, built with or into the universe. Strip away all the usual rules like omnipresence, omnipotence and omniscience, and we're left with a force which acts some of the time, succeeds some of the time and leaves the rest to physics. Far more plausible than an almighty Godhead.
It's possible, sure, but is it likely? Are there enough unexplained events in our lives to make us seriously think that some have no material explanation? Perhaps your life is full of incredible coincidences, through which you believe you are being guided. The trouble with coincidences is that we only notice the ones that happen; not the ones that don't.
Say you're walking down the street to the grocer and you bump into someone you went to school with 15 years ago, in another city. The chances of this event are incredibly small, so it seems like destiny that you two would meet again here.
The thing is, how many people were there at your school? How many other people do you know, and how many of them might you have bumped into today? What about a stranger wearing the exact same clothes as you? Or your childhood hero whom you've never spoken to? Could there be a car crash right next to where you're walking? Could bird droppings fall right in front of your face and ruin your shoes? Or a meteorite?
There are an infinite number of possible events which might happen to you at any time and which you would regard as coincidences, or serendipitous. The probability of each one is almost nothing, but the probability of all of them simultaneously NOT happening is just as small if not smaller. A large amount of coincidences is practically certain for anyone on this planet. Even if you seem to experience more coincidences than anyone else, remember that you're in a sample space of six billion people and some of them are bound to have a surplus. Today's mass media trumpets any unlikely event to the whole world and makes us feel like our world is saturated with the incredible.
When I see a coincidence, I remember how many other amazing things might be happening, but aren't. I don't need a higher power to explain anything. I just know that it's a big world with lots of people who live for a long time.
None of this disproves gods, of course. It just shows that a creator is unlikely and an intervenor is unnecessary. This doesn't bode well for any power which is both creator AND intervenor.