I forgot to add:

The lawn was dethatched two summers ago, and lightly dethatched again early this summer in an attempt to rake up my matted pine needles that fell over the winter.

I do not know if/when it was last aerated, or if it would be helpful.

Thanks-
L.

Contrary to what most "lawn experts" tell you dethatching is not necessary unless the thatch is more then 1/2 inch thick, and if the thatch is that thick there is a soil problem that needs to be addressed because the Soil Food Web is unable to function well. Whether grubs are a problem depends on the population, 5 or fewer per square foot are not a problem while 10 or more per square foot will be. In a good, healthy soil grubs will be kept under control by predators that will not be present in a sick soil.
Recycling your grass clippings can help because they can supply 1/2 the needed 2 pounds of Nitrogen per 1,000 square feet lawns need each year.
Your soil does need organic matter which will help retain necessary mositure, as well as provide a food source for the Soil Food Web that will feed the grass you want to grow.
Start by contacting the local office of your Washington State University Extension Service about having a good, reliable soil test done so you know what your soils pH and base nutrient levels are. These simple soil tests may also be of some help in getting your soil into that good, helathy condition needed to grow a strong and healthy garden.

1. Soil test for organic matter. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. For example, a good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drains� too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer your soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.

Here is a link that might be useful: WSU CES

GardenWeb has a rule against posting links or directions for people to go to competing forums for guidance. They do allow linking to non forum sites. Unfortunately none of them agree with me ;-)

Have you read the Organic Lawn Care FAQ on the GW Organic Gardening forum? It is near the bottom of their FAQ list.

It is my opinion that very little of what is in print and most of everything you can read on the web is based on information which is out of date. J.I Rodale was a very successful publisher back in the 1930s and '40s and is considered the father of organic gardening. Unfortunately he did not have access to modern science (since 1990). Thus his push was to use compost for everything. Up until the mass production of DNA testing facilities, soil science had stagnated. After DNA testing became "dirt cheap," it was discovered that there were thousands of times more invisible microbes living in the soil than anyone had predicted. In fact there seem to be around 100,000 distinct DNA types found in the soil. With that discovery the modern era of organic gardening began. And with that in mind, if there comes a competition to see who is the modern parent of organic gardening, I would nominate Dr Elaine Ingham. Now the reasons why compost works are understood. Furthermore the reasons why compost is not the end-all/be-all of organic gardening are understood. Compost is excellent at delivering all the beneficial microbes you need in your soil. It is not so good at feeding those microbes. Why? Because all the valuable food that went into making the compost is gone. Those microbes need more food. Thus the modern solution of feeding the soil has been established. They used to talk about feeding the soil with compost. Now they talk about feeding the soil with food. What food? Food with protein, carbohydrates, enzymes, vitamins, and minerals. Any food. The practical foods used in modern organic gardening are corn, wheat, soy, alfalfa, cottonseed, and a few others. These go on the soil at a rate of tens of pounds per 1,000 square feet. Other sources of protein have been tried with varying success. Of course the Pilgrims were taught to use fish in with their corn seeds. Modern day fish applications are limited to liquified fish remains applied as a spray. There is also some success with feather meal. Generally the animal based materials have an odor issue. Grain based materials normally do not although they can when overapplied. There are other schools of thought that you could feed your lawn with a spray-on type of material. These would go on at a rate of micro-ounces per 1,000 square feet. Personally I have seen the evidence that 10s of pounds of corn meal really works. How a fraction of an ounce of fish meal could do anything of value is a mystery to me.