The good news is that you're in the final countdown to seeding your lawn next weekend. The bad news is that this summer's just-ended grass seed harvest in Idaho, Oregon and Washington fell far short of the industry's forecasts, so the seed shortage that's plagued the home garden market for the last two years will continue for at least another 12 months.

What effect will this have on your residential lawn?

Seed prices have increased since spring, and they will move higher as the supply is exhausted by homeowners renovating their summer and fall lawns. Garden shops probably face occasional shortages of the most-wanted seeds, especially for the better-quality strains of tall fescue that have come on the market in recent years. Homeowners shopping for seed in late September will be shocked to find the retail shelf depleted of the better grasses.

The seed crunch translates into a shortage next spring, too. If you elected not to renovate the lawn this summer because you have plans of doing it next spring, you might want to reconsider. Aside from the l988 price hike, the seed supply will be limited by virtue of the increased volume of grass seed sales in late summer.

Meanwhile, last-minute preparations are in progress on lawns due for seeding next week. Make certain you have not overlooked any elements in your reconstruction program that would delay seeding unnecessarily.

The foundation of your program is ridding the lawn of thatch and debris. No matter which route you take in dethatching the lawn, the surface should be spotless when the last bag of trash is stashed at the curb for the sanitation crew. If you haven't dethatched yet, a good rule of thumb is 90 minutes for a lawn of 2,000 square feet.

When it comes to shopping for seed this week, don't buy old grass seed as shoppers did for years.

Here are a few factors to consider before you buy seed:

If you had a lawn with a 60-40 weeds-to-grass ratio, do you know the good grass remaining on the lawn? Just as important, are you really satisfied with it, or would you like to change? Ordinarily, you don't change horses in midstream, but with so many spectacular new grasses developed in recent years, why not try a high-tech grass for a change? For example, the newer tall fescues are so superior to Kentucky 31 that most homeowners would rather kill the old Kentucky 31 than live with an ugly lawn one more year. You still have that option.

If you had the disaster lawn and you're starting from scratch, the world is yours. You can grow any variety you want, but know what you're doing before you plant.

Not all grasses survive in all environments. Kentucky bluegrass needs full sun to yield a picturebook lawn; in shade, bluegrass gradually fades, especially if perennial rye is added to the mixture to hold the soil while the bluegrass germinates, which takes three weeks. Conversely, if your lawn occasionally has poor drainage and shows puddles of water after a storm, grass is probably not the answer. Landscape around the problem of wet soil; plant a red-twig dogwood, which loves to have its roots standing in water.

Not every grass loves foot traffic. If your lawn is in full sun and it's a playground for the youngsters, choose tall fescue. A mixture of blends will give you a lawn that survives baseball, soccer, football and volleyball and still comes through summer droughts smiling.

How much time are you willing to give the lawn? The secret in managing a spectacular lawn is doing things at the right time. If you don't have the time to do these simple things, then you want to find someone who will, and at reasonable cost.

Finally, if a lawn service has shepherded your lawn this year, this is a perfect time to evaluate its performance.

When you go shopping for seed, this is what you will find:

For lawns in full sun, choose from Kentucky bluegrass, tall fescue, fine fescue and perennial ryegrass. In terms of work, bluegrass will need the most care, tall fescue the least.

For lawns in partial sun and partial shade, choose from fine fescue and perennial ryegrass. Two Kentucky bluegrasses (Eclipse and Glade) tolerate as much as four hours' shade a day. Both fine fescue and perennial rye are low maintenance.

For lawns in dense shade, the only choice is rough bluegrass. You will need 90 to 100 percent shade to make it with this turf grass.

Which hybrid grasses are available this summer? We've checked the suppliers and these are the results:

Kentucky bluegrass: Adelphi, Eclipse, Glade, Merit, Nassau, Ram I and Touchdown. Features: medium to dark green color, survives bitter winter temperatures, also summer drought, slow to sprout, but yields a showplace lawn.

Fine fescue: Banner Creeping Fescue, Chewings Fescue, Jamestown, Koket and Pennlawn. Features: sprouts in 10 to 14 days, takes abuse from youngsters, has fine blades along lines of bluegrass, can stand neglect and barest of fertilizer application.

Tall fescue: Clemfine, Falcon, Houndog, Mustang, Rebel I and Rebel II. Features: withstands drought and heavy foot traffic, tolerates blazing Washington summer temperatures, sprouts in a week, best used by itself on lawn without mixing with other seed.

Perennial ryegrass: Citation, Derby, Palmer, Pennant, Pennfine, Prelude, Regal and Repell. Features: sprouts in a week, fine bladed, takes low cutting in spring and fall, tall cut in summer, grows rapidly and will crowd out every other competitive grass.

Rough bluegrass: Sabre. Features: keeps its dark green color the year-round, not going dormant during the winter, develops a dense stand in total shade conditions.

Since all seed is not the same, the rate of application will also vary on your lawn. Readers with 60-40 lawns are getting ready to "overseed" the lawn; that is, to apply seed over the existing lawn. Readers with disaster lawns have killed everything on the lawn; therefore, they will be using the rate for establishing a new lawn.

Here are the seeding rates for each 1,000 square feet of lawn area:

Kentucky bluegrass: 2 pounds for starting a new lawn, 1 pound for overseeding an existing lawn.

Fine fescue: 4 pounds for starting a new lawn, 2 pounds for overseeding an existing lawn.

Tall fescue: 7 pounds for starting a new lawn, 3 pounds for overseeding an existing lawn.

Perennial rye: 6 pounds for starting a new lawn, 3 pounds for overseeding an existing lawn.

Rough bluegrass: 3 pounds for starting a new lawn, 1 pound for overseeding an existing lawn.

When you buy seed, purchase one-third more than needed because you will want to overseed lightly after the new grass sprouts on the lawn. The extra seed will go down then to thicken the lawn in areas where the first seeding was thin.

Apart from seed, readers starting a new lawn on a slope should shop for a bale of salt hay before applying seed next weekend. Salt hay will be scattered on the lawn to prevent any soil erosion or seed washout during the germinating period. Salt hay will be left on the lawn and will decay over the winter to provide some minuscule nutrients to the soil. Salt hay, alias marsh grass, contains no weed seeds, repels water and softens the impact of rain on the lawn. Other products don't perform this way.

NEXT WEEK: Sowing the seeds for the lawn of your life.

Jack Eden hosts "Over the Garden Fence" Sundays from 10 a.m. to 1 p.m. on WTOP Radio (1500 AM).