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If your summer wanderlust is making it difficult to concentrate on work, consider this: Uncle Sam might pay for some of your unreimbursed business-travel expenses. As long as you are traveling primarily for business and will stay overnight, you can usually deduct not only the full cost of transportation but also lodging, incidentals like laundry and faxes, plus half your meal expenses. So before the summer ends, try to take a tax break by following these six guidelines:

--Put profits before pleasure when traveling Stateside. To write off the cost of a U.S. trip, you must be able to prove to the IRS that you had a legitimate business reason for visiting, say, Aspen, Colo. rather than Allentown, Pa. But you can mix work and play. If, for example, you have to go to the company sales conference in Phoenix, you can still write off the round-trip air fare if you tack on a couple of days afterward to go hot-air ballooning in Scottsdale, Ariz. Why? Because the primary reason for the trip was business. Just bear in mind that any costs incurred during those extra days aren't deductible.

--Keep track of time overseas. If you combine work and pleasure abroad, you can deduct all of your unreimbursed business-related expenses, including air fare and half of your meal costs, provided you meet the following conditions: You're ordered overseas by your employer or, if you are self-employed, a personal vacation was not the main reason for the trip and the trip either lasts one week or less or lasts more than one week but you spent less than 25% of the time on personal activities. If you devote less than 75% to business and the trip lasts beyond a week, you must prorate your costs according to the time spent on the job.

--Get your spouse working. The IRS ruled in January 1994 that you could deduct the cost of bringing along your spouse or any other relative on a business trip only if he or she is also an employee and if his or her presence serves a "bona fide business purpose." Since the IRS doesn't define what it considers to be a legitimate business purpose, consult with a tax adviser to find out whether your spouse's work would qualify for a deduction.

--Follow the custom on conventions. Being appointed or elected a delegate to a convention doesn't mean you can automatically deduct your expenses. The trip must benefit your business too. (So while journalists can write off the cost of covering the presidential conventions this month, representatives of Congress cannot.) A foreign convention is deductible only if the meeting is for business and it's reasonable to hold it outside North America. Sorry, you generally can't write off investment conventions or seminars.

--Carefully navigate the tax law on cruises. A meeting or seminar at sea is tax deductible (maximum amount: up to $2,000 a person) if it's directly related to your business. In addition, the ship must be one of the very few registered in the U.S. and you must sail to ports in the U.S. or its possessions, such as Puerto Rico, U.S. Virgin Islands and Guam. To claim the write-off, you'll have to attach a statement to your '96 tax return--signed by an officer of the group sponsoring the seminar--specifying the length of your trip, the schedule of business activities and the number of hours you attended the sessions.

--Keep superb records. You must have receipts for all lodging and any transportation, meals or incidentals costing $75 or more; the government will want to see these in a tax audit. It's helpful to take along a travel diary and record all expenses and the business reason or expected benefit from the trip. If you go overseas, note the foreign exchange rate, so you can convert those francs or yen to dollars. May you sail with the wind at your back and the IRS off your back.