On top of the general tax cut bill it has already promised to send Congress, the Reagan administration is preparing a second, more specialized measure for introduction this spring that, among other things, will propose big cuts in the maximum tax rate on dividends, interest and other "unearned" investment income, administration officials said yesterday.

This second bill also is expected to include equally controversial proposals to reduce some so-called tax expenditures, sources said. These are the assorted exemptions, deductions, credits and other forms of tax forgiveness in the code that now cost the Treasury more than $260 billion a year and benefit a broad range of individual and corporate taxpayers.

In political terms, a tax reduction on "unearned" income overwhelmingly would benefit upper-income taxpayers. Any move against tax expenditures, on the other hand, would be likely to hit these same taxpayers hardest.

The administration's plans for a second tax bill were disclosed yesterday by White House counselor Edwin Meese III at a private meeting of trade association executives sponsored by the American Society of Association Executives.

Meese confirmed that the tax bill that President Reagan will announce Feb. 18 will be limited to the 10 percent, three-year individual tax cut and an increase in depreciation allowances for business investment.

This strategy is designed to produce the fastest possible action on the initial tax bill, which is regarded as a vital part of the Reagan economic recovery plan. Then, two or three months after that tax bill has been introduced, a second will follow, recognizing that members of Congress have scores of their own tax proposals. The administration's hope is in this way to keep those proposals off the first tax bill, he indicated.

In response to a question, Meese said the administration was seriously considering a proposal to provide equal taxation of "earned" and "unearned" income. Currently, the tax rate on "earned" income such as salaries, professional and self-employment income, and pensions is limited to a maxium marginal rate of 50 percent, while the maximum rate on other "unearned" income is 70 percent. The administration is "definitely exploring" applying a 50 percent maximum rate to "unearned" income as well, Meese said.

"We're headed in that direction," he said.

A tax reform bill would provide the administration with an opportunity to demonstrate that its tax and spending proposals are not weighted to benefit the well-to-do and penalize poorer Americans, administration officials say.

Treasury Secretary Donald T. Reagan faced that issue yesterday in a televised interview with journalist Carl Rowan, who asked Reagan why the administration was cutting back on food stamp assistance and not doing anything about limiting the tax deductions that wealthy taxpayers can take for mortgage interest on second and third homes.

Regan said the cuts in food stamps wouldn't affect the poor. The limits in eligibility that the administration is planning will hit college students, who use food stamps to buy beer and liquor, Regan said. As to the mortgage interest deductions Rowan mentioned, Regan said the administration is "looking into" an "interest cap" -- presumably a limit on deductibility in this area.

According to congressional sources, the administration is considering restrictions on the use of industrial development bonds by localities to provide low-cost financing for fast-food franchises, shopping centers and other commercial development.

For several years, the Carter administration tried to limit the use of taxexempt financing, noting that its use had ballooned far beyond the original intent to assist the construction of schools, roads, and other publis facilities.

Last year, only about 35 percent of all newly issued long-term, tax-exempt bonds were used for public projects, with the rest going to finance private housing, pollution-control facilities for private industry, private hospital construction, office buildings, country clubs and private commercial development, according to the Congressional Budget Office.

Last year, Congress voted to phase out the use of tax-exempt bonds for single-family housing by the end of 1983, and imposed eligibility restrictions in the interim.

In its final budget proposal last month, the Carter administration proposed new restrictions on so-called "small issue" industrial development bonds worth $10 million or less, which have been used increasingly by state and local government to help finance business development, at a current cost to the treasury of some $1.6 billion. Congressional sources expect the Reagan administration also will move against this practice. Eliminating new bond issues for such purposes would save about $300 million in fiscal 1982, the CBO estimates.

It is not yet clear where the Reagan administration stands on the range of tax expenditures now available to taxpayers. These include: deductions taxpayers can take on interest payments on mortgages, which will reduce treasury receipts by $25 billion in the 1982 fiscal year; on charitable contributions, an $11.5 billion item, and payments for health insurance by employers, a $16.6 billion loss to the treasury.

The list of tax expenditures also includes such examples as the benefits for investors in oil and gas development projects, for companies that set up special export subsidiaries, and for timber companies and shipping firms.

Rep. James Jones (D-Okla.) observed last week that there would be tremendous political opposition to changing the deduction on home mortgage interest payments, but that it might be possible to pass a limit on deductions for interest on commercial loans such as those used to finance autos and major appliances. That expenditure is expected to total $6 billion in fiscal 1982.

Previous attempts to change tax laws in these areas generated months of debate in Congress and the reaction presumably would be the same this time.