TAX REFORM; How Treasury plan would affect individuals. . .

INDIVIDAL taxpayers as a group would come out ahead under the Treasury Department's tax reform plan, announced last week. Overall, 56.4 percent of American families would see their tax bill shaved under the plan, 21.8 percent would see no change, and 21.7 percent of US families would face higher taxes.

But the plan's effect on individuals would vary. Here is how the plan would affect you if you are:

A parent. You would be able to deduct $2,000 for each dependent instead of the current $1,090.

A homeowner. The plan would allow you unlimited deductions for mortgage interest payments on your principal residence. But such payments on a second home would be subject to an overall ceiling on personal interest deductions. That ceiling: $5,000, plus an amount equal to income from investments.

The Treasury plan ''will probably increase the value'' of primary homes because proposed changes in the corporate side of the tax code would reduce the incentives for developers to build apartments and condominiums, says Mario Borini, national tax director at Seidman & Seidman, an accounting firm.

The mortgage interest limit also ''could have a major impact on the home industry and the value of vacation homes,'' Mr. Borini says. His firm is advising clients with vacation homes to sell now. And if you are thinking of buying a vacation home, ''wait until 1986. You'll probably do well,'' he says.

But other experts advise against overreacting. First, the plan must clear Congress, an unlikely event, according to many observers. In addition, interest payments for many people who own vacation homes will still fall under the $5,000 ceiling, notes Robert Black, manager in the National Tax Office at Ernst & Whinney. ''I don't think anybody is about to take a bath on a vacation home,'' he says.

A local taxpayer. You would lose the deduction for taxes paid to state and local governments - levies such as real and personal property taxes, income taxes, and sales taxes, and some registration fees.

The effect of this provision would vary by locality, says Donald Ratajczak, director of the Economic Forecasting Project at Georgia State University.

There ''is something to the claim'' that the loss of the property-tax deduction may depress home prices in areas with high property taxes, says Harvey Galper, a Brookings Institution tax expert. This is because the after-tax cost of paying for the home would rise, thus depressing the price a buyer would be willing to pay for a home. As a result, individuals living in high-tax areas could feel the loss of the local-tax deduction twice: in a higher federal income tax bill and in lower property values. The impact will be less pronounced in low-tax areas, experts say. Some economists say some people may be tempted to leave an area with high local taxes if the federal tax code is revamped.

An employee. Premiums employers pay for your group life and legal insurance would be counted as taxable income. Employer-paid premiums on health and accident insurance would be taxable if they exceeded $70 a month for a single person or $175 a month for a family. The health-insurance cap would increase the taxable income of about half of those who receive some employer-provided insurance, the Treasury Department says.

People with major benefit packages, especially those who work in heavily unionized industries, will be ''significant losers,'' Mr. Ratajczak says. The change could also accelerate the trend for firms to try to hold down health-insurance costs.

A contributor to a church or charity. The plan would allow you to deduct charitable contributions, but only to the extent they exceed 2 percent of your adjusted gross income. Currently there is no floor on giving. And you would not be allowed to deduct the unrealized gain from property you contribute.

If a taxpayer ''feels an affinity'' for an organization, such as a church, and if it collects money weekly or monthly, such organizations should not be affected by the change, Mr. Black says. ''But there will be some reduction'' in giving to organizations that the taxpayer does not feel as close to or that solicit contributions only once a year. Experts also say that if this provision were enacted, people could tend to lump into one year perhaps two years' worth of giving to some groups in order to meet the 2 percent test.

Even if these provisions were not included in the Treasury Department's plan, your net cost for donating a given amount of money to charity could rise because of the reduced tax rates.

A stockholder. If you sell some stock or property, the capital gain would be taxed at the same rate as your regular income, after adjusting the asset's value for inflation. Currently, 60 percent of a capital gain is excluded form taxable income. And you could no longer deduct dividends. Currently, you can deduct them from income up to $100 for an individual and $200 for a couple.

The effect of this change will depend on a stock's appreciation rate, the current inflation rate, and the size of the dividend a stock pays.

If you hold stock with a low appreciation rate and good dividend payout, you might receive larger dividends, Mr. Ratajczak says, because the Treasury plan would allow companies to deduct one-half of their dividend payments from taxable income. That would encourage companies to raise dividend payments. But if you hold rapidly appreciating stock during a period of low inflation, you might pay a higher capital-gains tax if you sell the stock. Trading the old system's capital-gains exclusion for an inflation adjustment isn't going to help reduce your tax payment much, says Kennth Orbach of Ernst & Whinney.

COMPARING TAX RATES Single tax returns Under current law * Treasury Department plan Taxable Marginal Taxable Marginal income rate income rate Less than $2,510 0% 31,430-37,210 34 Head-of-household returns Less than $2,510 0% Less than $3,500 0% 25,650-31,430 28 $25,000 to 48,000 25 31,430-37,210 32 $48,000 or more 35 2Joint returns Less than $3,710 0% Less than $3,800 0%

* Estimated

Source: US Treasury Department, Office of Tax Analysis