Those nifty new tax cuts for business don't sound so nifty when the person you're talking to runs a small business.

As he sees it, it's the big guy with a stake in heavy equipment who really gets all the breaks. The little guy, whose biggest business cost is labor and who takes depreciation deductions in a low tax bracket, gets very little help at all.

Many of the personal tax cuts help small-business people. There are 10 million to 12 million proprietorships in the United States where business income is reported on the owner's personal return. Lower capital-gains taxes leave you more profit if your business is sold. Lightened estate taxes make it easier to keep a business in the family. But these changes affect personal wealth, not the productivity of your company.

Small businesses vary, of course. Some will profit considerably from the new rules. But others will find that the tax changes hardly yield enough cash flow to pay for the accountant's time.

Here are the new rules most likely to help small business, according to Kirk Dolby of the accounting firm of Peat Marwick Mitchell & Co. Most are effective on Jan. 1, 1982:

* Corporate tax rates. The rate in each of the two lowest brackets goes down one percent in 1982 and again in 1983. That's hardly a bonanza. On $25,000 of earnings, you will save $500 in 1983; on $50,000 of earnings, you will save $1,000.

* Subchapter S corporations. Here there is no corporate income tax. Shareholders declare all profits and losses on their personal tax returns, right along with their other income. This is especially useful to investors in start-up companies who can use the business losses to shelter other income. The new tax law raises the maximum number of shareholders allowed in a Subchapter S corporation to 25, from only 15 today -- a change that could help entrepreneurs attract more capital.

* Accumulated earnings. A good many small-business people accumulate money in their companies, either for future business needs or as a personal tax shelter. The company pays taxes on its earnings (often in a low bracket), but as long as they aren't paid out in the form of dividends, the owner can avoid personal income tax on what amounts to his share of the profits.

The IRS requires that these accumulations be "reasonable," above a certain minimum level -- an attempt to keep people from using corporations as a way of ducking personal taxes. That minimum level -- a safe haven for earnings accumulations -- has been raised for most corporations to $250,000, from $150,000. (Exception: Personal service corporations -- in health, law, engineering, architecture, accounting, actuarial science, performing arts and consulting -- are still held to the old $150,000 limit.)

* Inventory accounting: LIFO valuation -- "last-in, first-out" -- reduces taxable income in inflationary times. But it calls for a complex accounting system, often beyond the capacity of a small company. The new law simplifies LIFO rules for companies grossing around $2 million or less. If you're not using LIFO, it's worth a talk with your accountant to see if you should switch.

* Leasing: Companies that can't afford to buy the equipment they need should now find it simpler to lease. Other companies may tax-shelter income by going into the leasing business as a sideline.

* Small change: (1) You may write off up to $5,000 on a capital purchase right away, rather than spreading out the entire cost over a stated number of years. (2) Unprofitable businesses may carry forward their unused tax credits and deductible losses for as long as 15 years (up from seven years today), to tax-shelter whatever earnings might eventually turn up. (3) You may take an investment tax credit on the purchase of used equipment costing as much as $125,000, up from $100,000 today. This ceiling, and others in the law, are scheduled to rise in future years.

But prosperous business does not live by tax favors alone. "Tax credits for capital investments are fine if you can get the money you need to make investments," says David Kramarsky of the National Small Business Association. "The cost of money today is prohibitive. This is a terrible problem for small business and is not addressed in the president's new tax bill."