SUCH are the rights of life in the information age that I have devised a routine for sorting through the daily mail. I divide it into five piles. Grade ''A'' junk mail goes straight into the garbage, unopened. Especially those oversized, overstuffed envelopes tempting me to probe their contents. Grade ''B'' junk gets opened, sometimes against my better judgement. Those book club offers, for example, beguile me every time. The third pile is bills. As much as I would like to lump them with the first two, I dare not. I've tried it, and it simply doesn't work. They just reappear. Finally, the letters and packages generated by human beings, rather than computers, and requiring a customised response go into piles four and five. One is for business matters, the other for personal. I was performing this ritual last week when I came across a striking red envelope from MCI, the long-distance telephone company battling it out with AT&T and my own carrier, Sprint. I was about to consign it to the Grade ''A'' junk heap when something caught my eye: a proverb on the envelop - in Chinese. ''Good things come in pairs,'' it read cryptically. ''Something to satisfy both parties.'' Inside I found a form letter written in English on one side and in Chinese on the other, signed by Rose K. Lee (a.k.a. Li Hongsi), Asian Marketing Manager. ''We all have countless good reasons to call friends and families back home,'' Ms Rose began, alluding to my non-existent Asian roots. Then she went on to offer deep discounts on international calls to Taiwan, Hongkong and mainland China. Which got me thinking how MCI knew I frequently call these places. I decided to find out and, over the next two days, I played an elaborate game of pass the buck (Beijingers call it ''kicking the leather ball'' - ti pi qiu) with a string of polite but edgy operators, supervisors and ''customer service representatives''. One of them, Chad Bisinger, gingerly asked if I subscribed to any Asia-related magazines, or had travelled in that part of the world recently. No, I assured him, MCI must have bought the information elsewhere. ''The local phone company, by any chance?'' I wondered out loud. Mr Bisinger fell silent. Perhaps he knew, as I do, that Federal law prohibits phone companies from divulging confidential information, such as how many calls someone makes to which countries and when. He decided to punt, and suggested I talk to one of his colleagues upstairs. In the end, after my query was ''escalated,'' I got back word: ''It is not possible at this time to make a determination as to the exact source . . .'' In other words, ''We don't know or we're not saying - take your pick.'' MCI is not saying. Though indeed connected to Asia in myriad ways (apart from magazines and recent travel), I know the information came from my supposedly private phone records for one reason: the MCI letter was addressed not to me, but to the man from whom I rent an apartment and whose name appears on my local phone bill. Wherever else Mr Coffin has been in the world, he has never been to Asia. Nor does he have any Chinese speaking relatives, at least none that he is aware of. Though unable or unwilling to divulge the source of its information MCI did refer me to the Telephone Preference Service (TPS) and its counterpart for mail. These outfits, both operated by the Direct Marketing Association (DMA), help consumers suppress their names from telemarketing and mailing lists ''to decrease the amount of national commercial calls received.'' THAT is a much needed service, but the provider hardly inspires confidence. The DMA is not a friend of privacy. Even in touting the TPS, the Association insists that ''experience has shown that many people enjoy receiving information about products and services in their homes over the telephone.'' On incoming calls? Show me one. Guerilla fighters in the movement to protect individual privacy have formed their own organisations, and they are getting very busy indeed. Some of them belong to the United States Privacy Council, an advocacy group formed last year to hold the line against inquisitive credit bureaus, consumer investigative reporters and the federal government. They have plenty to worry about. Interconnected computer systems contain so much personal information - detailed records of our credit and employment histories, medical information, purchases, travel itineraries, even grocery lists - that can be accessed by almost anyone plugged into the right network. One company, Equifax, which sells such information to prospective employers and insurance companies, boasts that it has files on more than 170 million Americans. Though Equifax has been investigated by federal regulators, they operate in a system that imposes very few constraints. As telephone systems become more sophisticated, as the FBI lobbies Congress to make it technologically easier to conduct wire taps, and as information brokers compile files on individuals that would be the envy of Big Brother himself, privacy will becomean end-of-the-century battle ground.