Clean Out the House, Cut Taxes Simultaneously : Deductions: Charitable donors sometimes cheat themselves by ignoring favorable IRS rules.

Searching for year-end tax deductions? Look in your attic, basement or garage.

Old clothes, books and household goods can be worth hundreds of dollars on your next federal income tax return if they are donated to qualified charities by Dec. 31 and adequate records are maintained.

“If you haven’t worn . . . or used it . . . in a year, then go ahead and donate it,” said William R. Lewis, a Lincoln, Neb., accountant who has developed “Cash for Your Used Clothing,” a booklet listing market values of nearly 600 items of used clothing and household goods.

The Internal Revenue Service lets taxpayers claim as an itemized deduction the “fair market value” of donated property, which means what comparable items would sell for in places like thrift or consignment shops.

The government puts the burden of determining that value on the donor, not the charity. Moreover, if the value of all the donated property exceeds $500, taxpayers must fill out extra paperwork--Form 8283. An outside appraisal is required if the total value reaches $5,000 or more.

Few people, however, take the time to accurately calculate the value of their property or check out a charity’s background. The IRS says only about 10% of the 114 million returns this year included Form 8283.

“To avoid filling out forms, they’ll guess at a number less than $500. Unfortunately, they’re short-changing themselves,” Lewis said.

He says most people would be surprised by how much their discarded items might be worth if resold over the course of a year.

Among the examples listed in his 44-page booklet, which sells for $25: A man’s two-piece suit could fetch $15 in fair condition to $65 in good condition; boy’s jeans, from $2 to $7; maternity slacks, $3 to $9; books, 50 cents to $2; or an electric typewriter, $15 to $40.

Estimates are based on audits of several consignment and thrift shops in the Midwest and South; prices may be higher in the Northeast and West coasts.

“You probably can do a lot better than a garage sale . . . (and) it’s less time-consuming,” Lewis said.

In fact, Lewis said he first got the idea for his booklet several years ago, when his wife Karen announced she was planning a garage sale to eliminate some old stuff around the house.

“I had no desire to have a bunch of strangers go into my garage . . . just so we can sell a shirt for $1,” he said. “I said to my wife, ‘I’ll take whatever you’re going to sell to the Salvation Army and just write you a check for what they would be worth.’ I gave her a check for $400. I saved her a lot of time.”

Based on marginal tax rates, Lewis estimates households with annual incomes of between $36,900 and $89,150 can save 28 cents in taxes for every $1 in itemized deductions.

Non-cash donations totaling $1,500 for the year, for instance, could add up to a tax savings of $420.

They also add up to millions of dollars in revenue for the charities.

Goodwill Industries of America, which collects everything from cars to comic books, had revenue totaling $425.3 million last year from donated items resold to the public in its thrift shops, said Jeanne Hamrick, a spokeswoman for the Bethesda, Md.-based organization. She said Goodwill received 646 million pounds of clothing and textiles alone in 1992, or about 45 pounds per individual donation.

Like many other charities, Hamrick said Goodwill always has “a surge of donations” the final week of the year, since that’s the last chance to obtain tax deductions for the current calendar year.

The key to assuring the deductibility of a donation, though, lies in proper record-keeping. That means obtaining an authorized receipt from a charity and maintaining a list of the donated items, noting things like the original purchase price, current market value and condition of the property. Photographs or videos are also likely to stand up to IRS scrutiny.