If you are a homeowner or buyer with plans to turn some of your equity into cash, think about speeding up your timetable. Congress could surprise you with bad news if you wait too long.

Tax writers on Capitol Hill are sharpening their pencils again, and looking your way. Both the House and Senate have approved a federal budget requiring $19.3 billion to be raised in new taxes for the coming fiscal year. They have also agreed to impose $64 billion in aggregate new taxes during the next three years.

So where's the tax money to come from?

One area ripe for picking, says the congressional Joint Committee on Taxation, is home equity loans. In a report prepared for House Ways and Means Committee hearings this week, federal tax experts suggested five ways to get new money out of the home equity boom.

Topping the list is a proposal to ban deductibility of interest on equity loans unless the proceeds are used to rehabilitate, construct or acquire a first or second residence. Nothing else would qualify for interest deductions.

Put into practical terms, that means: If you're using your home equity loan to buy a car with tax-deductible interest, forget it. You couldn't deduct the interest anymore under the revised tax rule. Or if you're using your equity loan proceeds to pay for an expensive vacation, furniture or to consolidate charge account bills, the game would be over. No deductions for interest on the loan.

What is particularly attractive to federal money hunters about this, the report indicates, is that it raises big bucks fast. If the new plan were imposed on homeowners next fiscal year, the report estimates, it would raise nearly $4 billion in additional taxes between 1988 and 1990.

Besides new revenue, tax reformers suggest it would have the public policy benefit of "tend{ing} to limit interest deductions to situations where the incentives would directly encourage home ownership."

A second cutback on home equity loans proposed by the committee would be to limit interest deductions on loans used 2for noneducational or nonmedical purposes to $10,000 a year. That wouldn't touch as many people as the first. It would raise a mere $600 million from homeowner taxpayers by 1990.

A third and far more controversial attack suggested by the committee would be aimed directly at the fastest-growing form of home equity loans: revolving lines of credit with no fixed terms for loan repayments. These are the "equity lines" that banks and savings and loans have promoted so heavily in the wake of last year's Tax Reform Act. Once you're approved for credit tied into your real estate equity, you simply draw down your line at will.

Because the credit is secured by your personal residence, the interest is tax-deductible as long as the amount borrowed is limited to the basis in the house or spent on medical or education expenses. Under the 1986 Tax Reform Act, by contrast, interest on conventional consumer loans -- including charge accounts -- is nondeductible. Although the committee report offers no revenue-raising estimates, the new tax money during the next several years could be substantial. It would also put a severe crimp in the multibillion-dollar credit-line industry that has grown so rapidly during the past 12 months.

Two final proposals from the committee would touch a smaller number of people, generally middle-to-upper income taxpayers. The committee suggests eliminating interest deductions on loans for boats and mobile homes as second residences. For years, the federal tax code has permitted certain boats and mobile homes to qualify as legitimate second residences, provided they contain the full complement of cooking, sleeping and sanitary facilities found in any home. Fifteen-foot runabouts and cab-overs on pickup trucks never made the grade.

Suddenly shifting all boats and mobile homes into the nondeductible category would raise political hackles in all the major tourism and recreation-oriented states, while apparently raising less than $50 million in net new taxes.

The committee's last proposal would touch only the super rich. It would limit to $1 million the maximum amount of home mortgage debt that would qualify for interest deductions. Beverly Hills would howl at this one, but most people wouldn't give it a second thought.

What's the upshot of all this? Where are these tax recommendations headed?

Congress is irretrievably pledged to raise taxes. President Reagan has threatened to veto, but he might go along with some compromise budget solution. Whether the taxes on the horizon come out of homeowners' hides -- or someone else's -- could be determined by the end of July.