No matter how smoothly your lawn mower hums this summer, eventually the day will come when it coughs and sputters its way to the garbage heap. But is that an environmentally responsible way to discard it?

The Outdoor Power Equipment Institute suggests five ways to handle the disposal problem. First, decide if the machine can still be used or has some value. Then, choose the most appropriate method for disposal:- Donate it. There are many charities that may be glad to have old lawn and garden equipment if it has some life left - or if it can be repaired. The donation may be tax deductible.

- Sell it. If the machine is in fairly good condition, it may be worth placing a classified ad in the local newspaper or including it in a neighborhood garage sale. The object here is to find it a new home - not to make a mint.

- Trade it. People can often use old equipment to negotiate a deal at a specialty retailer (mass retailers and department stores probably won't be interested). Check the Yellow Pages under "Lawn Mowers," or "Outdoor Power Equipment Dealers" to find dealers willing to accept the machine.

- Scrap it. Even if it doesn't work, old equipment may have value to a scrap dealer, who can salvage parts and metals. Call some scrap dealers (listed in the Yellow Pages) to find some who are interested. Most pay based on the weight of the elements they reclaim.

- Trash it. If the other options fail, it's probably time to call the trash collector. A pickup arrangement may have to be made. If the trash collector won't handle it, call the state solid-waste management agency for help.