TAX EVADERS and other lawbreakers who want to avoid records of financial transactions deal in cash. Checks, credit cards and charge accounts leave tracks, but currency goes from hand to hand anonymously. Big league crooks are said to be especially partial to the hundred dollar bill, because it makes manageable bundles.

Last week, the National Law Journal obtained a copy of a confidential memo sent by IRS Commissioner Roscoe Egger to Treasury Secretary Donald T. Regan. The memo, the contents of which have been made public by the journal, is an 88-page compilation of new enforcement measures the IRS would like to use to collect from tax cheaters. Much of the wish list is fairly technical, involving interest payments on seller-financed mortgages, for example. But the section on what to do about hundred dollar bills makes fascinating reading. Did you know, for example, that 40 percent of the $125 billion of currency in circulation is in hundred dollar bills? If you haven't seen any of them lately, it's because most of the bills seem to be passed from hand to hand in a select community described in the memo as "those who need a highly liquid, anonymous form of wealth, something that can be secreted in an ordinary envelope or stuffed in a suitcase. They include tax evaders, drug traffickers, illegal gamblers, loan sharks fencers of stolen goods and corrupt politicians."

How can the IRS make it a little more difficult for these people to keep their money in currency? Well, they could call in all the hundred dollar bills and make it twice as hard to hide a wad of cash. It might work, but somehow we think the underworld would adjust and cope with the bulk. Another proposal is to replace all hundreds now in circulation with a new bill that would be easily spotted, and monitored by banks. Former IRS Commissioner Donald Alexander says that in the early '70s he wanted to make them pink--or too large to fit into a pers" for "fison's pocket, so a drug dealer carrying large sums of money "would weigh 300 pounds."

All this sounds like great fun, and Treasury officials themselve say that while the hundred dollar bill problem is a serious one, the proposed solutions don't appear to be too practical. We like the idea that the IRS is trying to collect from crooks and cheats so the burden borne by the average withheld, computerized and audited citizen can be shared. And if they do go so far as to print pink hundreds, here's a suggestion: change the portrait. We doubt most feminists would want to be honored on a frilly bill, but it's a good bet Phyllis Schlafly would find it a much more appropriate way to honor women than adoption of the ERA.