THIS MASSIVE TOMBE is not so much a book as an investment. To haul it across the room is like moving the furniture around. To read it from cover to cover . . . Well, not even the author would suggest you go that far. You're meant to park it on the shelf somewhere between the phone book and The Joy of Cooking and haul it out when you need help -- which is probably sooner than you think.

With her six previous books and a daily newspaper column read all over the world, Sylvia Porter has become a sort of live-in fiscal den mother, striving for decades to translate what she calls the "bafflegab" of everyday economic life into terms that plain people can understand, and to guide the ignorant and gullible through the dark jungles of banking, insurance policies, mortgages, warranties and leases, as well as birth, marriage, death, taxes and all the other pitfalls of the human condition. The potential for trouble, you realize as you read her work, is so staggering that it's a marvel any of us muddle through at all. And her willingness to grapple with every coneivable phase of consumer life -- from buying a house to losing weight and choosing a contraceptive -- is both the wonder and the shortcoming of her work.

The present volume is a revised and updated version of the Money Book published in 1975 -- and the years have taken their toll. The first book set out to help the reader "to win in every sphere of your economic life." The new edition finds us all "frightened, guilty, confused," and offers to help us "avoid such futile fumbling." The major changes involve a new lead section on inflation (buttressed by the extra $5 it now costs to buy the book), plus new material on the effects of inflation wherever they occur -- from buying a car to planning your old age. Her advice on which months are best for shopping bargains has grown from 23 items (Back-to-school clothes to Toiletries) to 89 (Air conditioners to Water heaters). Her household energy-saving hints have expanded from heating, lighting and cooking to doing the wash. "If everyone washed clothes in warm or cold water we'd save the equivalent of 100,000 barrels of oil a day, enough to heat, 1,600,000 homes through the winter."

She gives fuel-saving tips for drivers; fresh advice on renting cars, and an expanded section on buying and using a bicycle -- which committed bike nuts will still find rather thin. Amtrak, which got high travel marks four years ago, has been downgraded and chopped back -- as in real life.

Otherwise, the basic overhaul seems to have been to dismantle the old volume, plank by plank and shuffle the sections into a different order, without any changes in the text. So as old Money Book readers can tell you, you learn a lot -- but you don't have much fun. Still, if you want to know how to buy furs, or shoes or boats (start with a year's subscription to Yachting or Boating ); or how much it costs to get married, have a child, get sick, die and be buried, just keep reading -- and allow time for naps.

She tells you what your rights are and where to send your complaints. She tells you how to save money on the long distance phone. (Dial your calls and keep it short.) She gives useful and lucid advice on everything from planning a budget to banking, saving and investing money. She tells you how to fight the IRS over a tax ruling; how to set up a retirement fund, find a lawyer, make a will, buy insurance, have an abortion and get a divorce. She outlines your options on finding a place to live; how to case the neighborhood and check for flaws. She spells out whether it is cheaper to buy or rent, depending on your tax bracket. If you move, she tells you how to do that -- from choosing a mover to packing your clothes. (Don't have more than two cartoons of "miscellaneous.") If you're painting a wall, "start at the upper left-hand corner and work down toward the floor." (If you're left-handed, start at the right.) She evaluates diets, health foods, furniture, appliances, antiques, contraceptives, contact lenses and Series E government bonds.

Trudging through this fathomless catalogue of perils and possibilities, you begin to wonder if there isn't more between these covers than the ordinary citizen ought to be told. After we've filled out four budget charts and noted all the grocery prices on 3x5 cards in the kitchen, do we still have to worry about what "Class" we belong in -- "Affluent," "Upper-Middle," "Average" or "Below Par"? If people have to be told to shop for clothes that are becoming and to sit on a chair before they buy it, do they deserve to be saved?

These are rather puny complaints in the face of the stupendous dimensions of this work. But there must be something wrong if the most routine elements of everyday life have become so complicated that we need a Sylvia Porter to explain them to us.