Thinking of shucking off winter's icy grip and heading for a few days of sun and sand a little closer to the equator?

Maybe you just got a brochure in the mail offering all this along with something that makes it even nicer - a tax deduction.Well, if it sounds too good to be true, the Internal Revenue Service would like to assure you that it is.

In fact, charitable organizations, professional organizations and other groups, many of which have found it more difficult to raise funds in the era of lower tax rates, have turned to tour operations as a major source of revenue.

They are taking advantage of the fact that under certain circumstances, travel expenses to provide services for a charity can be deductible as a charitable contribution.

And travel in connection with a trade or business, including educational meetings, can be deducted as a business expense.

But the rules are strict, and as more and more organizations are starting to offer tours that are nothing more than tax-deductible vacations, the IRS is cracking down.

"We're coming across more and more of them each day," said Robert I. Brauer, assistant IRS commissioner for exempt organizations. "We do not know exactly the scope of it right now," he said, but "we think it's widespread."

Another IRS official said, "They're coming out of the woodwork."

And the offenders include "some of the most reputable charities in the business," which "either wittingly or unwittingly get involved" in setting up tours involving improper deductions, Brauer said.

Some of the marketing has been so aggressive that IRS officials themselves have gotten solicitations for junkets featuring questionable deductions.

To combat the new wave, the IRS is attempting to publicize the rules for tax-deductible travel, focusing primarily on the tax-exempt organizations involved.

"There has been tremendous misunderstanding here, and a great need for education," said Howard M. Schoenfeld, IRS special assistant for exempt organization matters. "The commissioner and the service are saying the time has come for charities to clean up their act."

Brauer also pointed out that two different types of deductions, and thus two different sets of rules, are involved.

One type of deduction is for trade or business. Domestic travel of this sort is fully deductible if the primary purpose of the trip is connected to a person's trade or business, noted Gayle W. Herndon, special assistant to the IRS deputy chief counsel.

In addition, if part of a trip is legitimately connected to one's trade or business, expenses stemming directly from that part of the trip are deductible, even though other expenses, such as air fare from home, may not be.

In other cases, the deduction is for charity. This may be couched in terms of service to the charity - counting porpoises in the Caribbean for a wildlife preservation group - but as Brauer pointed out, "If there is a significant element of personal pleasure, recreation or vacation, it's not deductible."

Sometimes promoters combine the two. "The typical scenario would be an organization, a profit-making travel outfit, soliciting lawyers to go on an overseas trip to meet with their counterparts in the foreign country - on that basis promising a (business) deduction, and indicating also in the letter that if you care to bring along a spouse or a companion, we have a provision for an educational scholarship or a foundation that might entitle the spouse or companion to deduct (as a charitable donation) a portion of the cost of their trip," Brauer said.

"So there are different standards," he added. "It's very difficult for the individual to figure out what's going on. So that's one reason why our approach is to go after the charities, to go after the travel organizations . . . and basically say, `Look, you have to do a better job of informing the folks you solicit for these tours as to the extent of deductibility as to the rules and that sort of thing."'

In addition, just because you buy something from a charitable organization doesn't mean the price is deductible.

Schoenfeld pointed to a case in which someone donated the use of a ski lodge to a charity. The person who then leased the lodge may have thought that because he was paying the money to charity, the cost was deductible.

Not so, Schoenfeld said. The price he paid was the market value, so none of it was deductible. Only if you pay more than market is anything deductible in such a case, and then it is only the excess over market price that can be written off.