"What will it cost me?"

That's the question millions of taxpayers have been asking ever since October, when Congress hiked taxes as part of its five-year, $500 billion deficit-reduction package.If you don't like the bottom line, be prepared to get serious about long-term planning. Gone are the happy days when a March write-off-hunt was all you needed before filling out your 1040. Beginning this year, you have to adhere to three broad guidelines.

- Don't waste time chasing after increasingly trivial itemized deductions. Long-cherished write-offs have disappeared. (Among the lost: deductions for interest on personal debts).

- Make long-term commitments to tax-deferred accounts. Financial advisers urge clients to contribute as much as they can to tax-deferred accounts, such as 401 retirement plans and deductible IRAs, to invest in high-quality tax-exempt municipals bonds or bond funds and to make a maximum use of tax-cutting trusts in their estate plans.

- Count on taxes rising again well before 1996. The 1996 date is when the current budget projections expire. By then, we will know just how over-optimistic Congress' economic-assumptions may turn out to be.

The following 11 steps will help you in sound tax planning, whatever your income or tax bracket.

1. Put every penny you can in tax-deferred retirement savings plans. The simplest way is to make maximum contributions to a 401 plant at work. In 1990, the law authorized your employer to let you stoke a 401 with up to $7,979 pretax. Earnings grow tax deferred until withdrawn after age 591/2.

2. Open a flexible spending account (FSA) at work. Next to tax-deferred retirement plans, FSAs are our best shelter, enabling you to pay medical and dependent-care expenses with before-tax dollars. With an FSA, the law allows you to earmark as much as $5,000 for care of your children and other dependents.

3. Moonlight. The tax breaks made possible by burning the free-lance oil can significantly offset the tax you'll owe on the extra earnings. You can shelter as much as 20 percent of your self-employment income after deductible expenses annually in a Keogh retirement plan or in a combination of a Keogh and a simplified employee pension (SEP).

4. Give income-producing assets to your children. Every child under the age of 14 should have an account in his or her name that earns up to $500 a year. Reason: annual earnings of up to $500 are tax-free because of the child's standard deduction.

5. Consider tapping your retirement stash. With tax rates just about guaranteed to go up, now may be an opportune time to withdraw money from your tax-deferred retirement plans. If you're under age 591/2, you can avoid the 10 percent early withdrawal penalty by arranging to take the money in equal annual installments according to IRS life-expectancy tables. You must continue the withdrawals for five years or until age 591/2, whichever comes later.

6. Watch out for the alternative minimum tax (AMT). This arcane levy is imposed on filers whose tax breaks reduce their bill below an amount considered their fair share.

7. Pay off your consumer debts. Beginning with your 1991 return, you cannot deduct any of the interest you pay on credit-card balances, car loans and other borrowing.

8. Consider buying municipal bonds or bond funds. The higher your total income tax burden, the better tax-exempt munis look. Top-quality munis currently offer yields of around 7 percent, free of federal and usually state and local taxes if you live in the state where the bonds were issued.

9. Investigate tax-deferred annuities for retirement savings. Annuities may make sense if you meet these conditions: you are in the 28 percent or 31 percent federal tax bracket, have at least $10,000 to invest, plan to retire in 10 or more years, and have maxed out on other tax-favored retirement savings plans, such as a 401 or IRA. You get to sock away money that grows tax deferred until withdrawn.

10. Turn gift-giving into a habit. Bestowing money and property on others within the $10,000 annual limits to as many recipients as you wish ($20,000 if you give jointly with your spouse) while you're alive removes the assets from your estate, thus reducing its value and lowering eventual estate tax.

11. Consider setting up charitable trusts. These trusts let you reduce your taxable estate by donating assets to a charity. At the same time, you can get an income tax deduction for the value of the charity's interest in the gift.