Paul, you will have a difficult time keeping a lawn planted in June alive through the hot summer. On the other hand your suggestion of planting now to avoid loosing topsoil is an important concern, as well as controlling weeds there. Much of the grass that you plant now, you will probably loose. But do plant something and then plan on another planting first of September. Annual rye, which will die out in the winter should grow from seed now if you can water it frequently after planting and throughout the summer. Fescue grasses, both tall and fine germinate fast and some of it may survive if watered. Decide what variety of grass you want there. Buy the highest quality seed you can find and mix it with 50 % annual rye for your June planting. In September, cut it short and overseed heavily with your desired grass seed. This was a brief answer. Keep reading the posts here both current and past. A lot of information is available to you here from some very knowledgeable persons. Welcome to the lawn forum and good luck on your project.

Well, you've painted yourself into a corner as far as the timing goes. Whatever you plant now will take quite a beating in summer and much of it will die. Is this area small enough to keep watered regularly? If so, I would try to plant whatever grass mix you choose, water, and hope for the best. They sell a product called tupersan that you can use when seeding that will keep weeds from growing. If you didn't really kill off some of the nasty undergrowth weeds, they might regrow from the roots though. Definitely plan on reseeding in late summer/early fall because whatever you do, you are going to have problems to fix.

paulsju, there must be a groundcover which:-
Grows from seed.
Is quick growing.
Will stand the dry heat of summer.
Will be killed by the winter.
Hopefully it will be priced to be worth your while.
After all, this is America and there is an opportunity in every problem!

There is another concern, that you may or may not have heard of, and that deals with the soil's natural bacteria and fungus.

If you have a woodland, there is a type of fungus that grows naturally, and a type of bacteria that grows naturally, let's call them Type A.

On an established lawn, there is a natural type of fungus, and of bacteria that grows naturally, but the problem is that they are Type B.

Now that the woods are torn down, there is plenty of Type A fungus beneath the soil, but not Type B, which you need.

Mycorrhiza is the specific type of fungus that you need: it attaches (grows from) the plant roots, outward into the soil, and helps the roots do a better job. Google that word, and you can find a lot of articles about it. Here's a link to Bio-Vam, which is a product that I have used, with great success. My office lawn was installed with topsoil that had apparently been sitting around in a bin somewhere for a year or two, and nobody could grow a lawn on that soil. I had just moved into the office, and, purely coincidentally, had just read an article on mycorrhiza fungus, and a highway project, and the difference it had made. Short version of the story (I'm leaving out the secret spray of the product in an evening, then openly declaring, next day, that no one had ever toasted the lawn gods with Irish whiskey, and made the partners come out to do it with me) was that there was a noticeable difference in seven days, and an outstanding difference in three weeks.

I am convinced, totally, on the subject of mycorrhiza. I recommend Bio Vam only because it's the only product that I have used. I don't know if it's expensive, nor if it's cheap. It's the only one I have used. But I would seed the lawn, let it sprout, and spray the mycorrihiza. I would also fertilize with Milorganite, or some other sewage-based fertilizer product (there are several brands available on the East coast), as they won't burn the lawn.

It's true you're going to lose some percentage of that seeded lawn. Fifty percent? Twenty Five? Ten? If you planted in the fall, you would also lose some percentage of that lawn. A lower percentage? Probably. But it's a function of how well you are able to keep the seed, and then those seedlings, moist but not wet. Keep the hose and nozzle moving, no puddling allowed. No puddles.

But most new grass plants are lost when they're about the height of a dime (the ten cent coin) laying flat on the ground. At that height, they can dry out in an hour or two, less if there's a hot sunny, windy day. There's no root to let it grab moisture (the root hasn't grown yet) so there's no sense in any 'deep' watering. Just mist it. But if you do that, then when tomorrow gets here, that little plant will be a little more healthy, a little more tall, with a root a little more deep. And the next day. And the next day.

Good luck with it.

Here is a link that might be useful: Bio Vam mycorrhiza fungus