Absolutely.

sure. My step dad will pile leaves up on his garden and throw other stuff on it during the winter and will till them in during spring and he has no problems growing a garden. I plan on using leaves as a ground cover during the winter and taking the top ones that aren't being decomposed and throwing them in my compost in spring and tilling in the rest.

Since those leaves would make a very good mulch which would help protect your soil from the ravages of the weather, why would you want to till them in at all? Shredded leaves spread over the garden and left for a mulch will, eventually, be incorporated into your soil for you by the Soil Food Web with no more energy expended by you. If you use a powered tiller you are using an energy source unnecessarily.

If the leaves are of size such as maple or oak, be sure to chew them up well before introducing them to the garden and till them in well.
Materials as they break down do use nitrogen, but you can easily make up for that by simply feeding some nitrogen to the garden at the same time you add the carbonaceous leaves.

If you just spread them ontop, what have you got...besides a job cleaning them up again when the wind blows them?
Well, the worms sure aint there....they are down below the frost line. What are the leaves supposed to be doing?
They wont break down so they cant become part of the soil until well ingesting of moisture.
How many times have we left leaves on our lawns and gardens, had them go through a winter and find they haven't moved when the snow finally melts.

If you cant till them in, give them over to a compost pile--chew them up before adding, add some nitrogen fertilizer and spread them out and in the late spring, they might amount to something.
No compost pile....bag them, chew them up, bag, add some fertilizer, some water, poke holes in the bottom, lay them on the ground to let worms in and next summer you will have some great leaf mold for your flowers and roses.

I am not sure where the concept came to be accepted that decomposing leaves tilled into the soil will "rob" plants of nitrogen. This is not the case. In fact, it is only a concern when you are incorporating wood based materials (wood chips, sawdust, bark, etc) into soil and only as it applies to annual or very shallowly rooted plants. It has virtually no affect on larger, established woody plants like trees and shrubs. And even wood products will not have any significant impact on nitrogen availablity if they are used only as a mulch or topdressing and not incorporated into the soil.

Leaves left on top of the soil over winter do form an effective mulch and while perhaps not fully broken down or decomposed by spring, they will be well on their way. Because they are such an effective layer of insulation, worms and other soil organisms are often active right through winter at that juncture of leaf mulch and soil. Gather and spread them early, wet them down well and you have an excellent, free, soil-enhancing/biology-stimulating winter mulch for any planting situation.

As to adding of fertilizer to compost, composting leaves or to mulch, it just ain't necessary :-) There is no evidence to support that it speeds up the decomposition process and we tend to make a bigger to-do about nitrogen depeletion than is appropriate. Since this is the practice I've followed for all these many years I've been gardening, if fertilizing under these circumstances were necessary, my garden would be hugely nutrient deficient - I've not used or needed to use any fertilizer (other than compost or rabbit manure) in my garden for more than 20 years.

I can not recommend it enough. I do it every year and it keeps my soil filled with organic material and worms. However, as mentioned above, I combine the leaves with grass clipping for coffee grounds from Starbucks to make a mini compost pile.

I used to put about 4" of horse manure on top and let it leach into the ground over winter.Then in spring turn it under.
With this Salmonella scare I think I will now compost it first and add in the spring.

You might consider the 'Interbay' method of mulching. Look in the FAQ for this forum.

gardengal48, not to start an argument but it does take nitrogen to decompose material. Now confusing that with plain fertilizer is something totally different. Everyone knows that if they want to speed up their compost bin they must have nitrogen rich mater. I absolutely do NOT recommend using a nitrogen rich fertilizer to speed up composting because of the cost and processing energy that it takes to make it, but it does work. But when you till in whole leaves or carbon rich material or even unfinished compost it will tie up the nitrogen until it's done to a point that it will start releasing it to the plants. This is not such and issue with trees or bushes but can become an issue in vegetable gardens. That's why it's always best that you add some nitrogen material when you till it in like UCG or kitchen scraps or grass.

As far as you doing it for 20 years your garden already has a good establishment and I'm sure has no problem accepting heavy carbons as you have the microbs and worms there to brake things down quickly. As a newbie you have to either know your soil values or play on the side of caution and just add nitrogen rich material when tilling in leaves. Which is what he was already doing.

Below is an article on different types of nitrogen and how it can be tied up.

Here is a link that might be useful: Nitrogen info

The original poster also had a cover crop to consider...not just mulched leaves.

Unless the garden has never been tilled before, there usually is no real need to do that again. Buckwheat, grown as a summer cover crop, can be cut, or just knocked down (as long as the stems are broken) and left on the soil as a mulch and shredded leaves can be added to that and left and in the spring the soil will be ready to be planted in with some mulch already in place ready to aid in conserving soil moisture,suppressing "weed" growth, keeping the soil cooler during the hot summer weather, and adding organic matter to the soil, slowly, as the Soil Food Web works on that mulch, and they do a far better job of incorporating that OM into your soil then you ever could tilling it in.

My grandpa dumped out all his compost onto the garden every fall regardless of its state of doneness. In the spring, he tilled it in.

I know tilling is going out of style, but he had a great garden and I do it too, except I only till the bits that are still recognizable as unfinished.