During these times of double-digit inflation and soaring interest rates on loans, people with small passbook savings accounts are being severly short-changed.

Bank and savings institution interest rates are set by law and these rates now are generally around 5 percent on passbook accounts. Meanwhile, you have to pay close to 10 percent on a home mortgage and from 12 to 18 percent for consumer loans.

The banks and savings institutions are, in a sense, buying a product (money) fo r 5 percent and selling it for two to three times what they paid for it. Your passbook savings are considered "cheap money." You are subsidizing enormous markups on some loans.

Because the rate on passbook accounts is so low, people are wising up and are not putting as much in the kitty. Some are even taking their money out. Banks and savings institutions are complaining they won't have enough cheap money to keep on making mortgage loans.

So, why don't they raise the rate on passbook accounts? They keep this artificial rate pegged low because Congress won't change the law. And Congress won't change the law because the savings institutions and some banks don't want higher rates. They fear competition. They want to keep on raking in cheap money through passbooks.

But Congress is certainly kind to the big-money savers - people and businesses with $100,000 or more to play with. If you have $100,000, you automatically become a higher-class citizen as far as savings rate regulations go. You're allowed to negotiate your own rate - there's no limit.

Recently, people with $100,000 or more have been able to get up to 8 1/2 percent for short-term "jumbo" certificates. If you have $10,000, you can buy money-market certificates based on the government's Treasury-bill rates. The rate on these $10,000-minimum certificates has been close to 8 percent. The only limit here is the rate paid on the high-flying government securities.

The game is rigged by "regulation Q." This onerous regulation artifically sets a low rate on passbook savings, which are used primarily by lower-income people, while allowing the wealthy to rake in much high rates.

The rational is that the lower income people, being less sophisticated and beasts of habit, will continue putting their money into low-interest savings accounts while the wealthy, knowing they can get more elsewhere, have to be attracted by higher rates.

Passbook savers can get a little better deal in other areas - but it isn't easy. Credit unions, for example, are allowed to pay up to 7 percent on passbook accounts. But you have to belong to a credit union. Neighborhood and community groups are now forming their own credit unions with as few as 200 members and a few hundred dollars start-up capital.

Savings bonds pay 6 percent, and you need only $18.75 to buy a bond. But, to get the 6 percent, you have to leave your money in five years. Still, you don't pay state and local taxes on saving bonds, any you can defer your federal tax until the bonds are cashed in .

Money market mutual funds are now paying in excess of 7 percent on investments that work very much like savings accounts. You're paid interest from day of deposit to day of withdrawal and can take your money out any time without a penalty. There's no sales charge.

But, most funds require a minimum of $1,000 initial investment some require only $500. You can get fund addresses by writing Investment Company Institute, 1775 K ST. NW. Washington, D.C. 20006.