If you're one of the millions of Americans who own vacation property or maintain an office in your home, you're likely to be affected by new federal tax regulations proposed here last week.

The IRS on July 29 unveiled its long-delayed, much-revised standards for deductions on the business use or rental of dwelling units. (The rules also affect all joint-ownership and equity-sharing agreements on residential real estate, both to be covered next week.)

The new version of the vacation-home and office-in-the-home rules should provoke far fewer headaches and controversy than did the first set of standards issued by the IRS nearly two years ago. The August 1980, proposals were considered so extreme by homeowners and real-estate industry groups, in fact, that Congress expressly directed the IRS to ease up next time around. The latest standards represent the federal government's attempt to do just that--without giving property owners a blank check on deductions.

Take the sticky issue of "personal use" of a vacation rental home. Under the IRS' earlier proposed rules, a beach-house owner who needed to repair the unit's roof prior to summer rental would be construed as making personal, non-business use of the property if he brought along his teen-age son and daughter and they didn't spend eight hours at hard labor on the unit, alongside him.

Any personal, pleasurable use by a member of the owner's family--even if the owner himself slaved away nonstop for 24 hours painting and caulking the place--would register as personal use by the owner, said the IRS. (Under federal law, owners of vacation property are restricted in their tax deductions any year in which they personally use their units more than 14 days, or more than 10 percent of the days it's rented out.)

Second-home owners who look to seasonal rentals to help cut their annual costs, in other words, have a strong tax motivation to limit their own use--or at least limit any use that might fall within IRS' audit gunsights as personal. Visits to units to maintain and repair them for rental purposes traditionally have allowed the owner's family a weekend or two per year of fun at the beach house or ski condo, without triggering federal tax problems.

The proposed IRS guidelines provide owners plenty of latitude on their periodic "maintenance and repair" visits. Backing away from its Draconian standards of 1980, the IRS no longer will count property owners as having made personal use of their vacation homes if the "principal purpose" of their presence at the house "is to perform repair or maintenance work on the unit."

The IRS will look to "all the facts and circumstances" relating to owners' maintenance visits in making its determinations, including:

How often an owner makes such visits during the course of the year. (In other words, an owner who visits his ski chalet in Vail twice a month during high season to keep the heating system in good repair and the snow off the roof will have trouble passing muster at tax time.)

How much of the day was actually devoted to repair or maintenance work. (A little painting touch-up after breakfast for an hour followed by five hours on the beach probably won't convince the IRS, but the agency doesn't specify how many hours would.)

"The presence and activities of companions." An IRS source emphasized that companions--whether related or not--are fine, as long as the principal purpose of the visit to the unit can be documented as maintenance and repair. You can bring your friends to the chalet to play, as long as you mainly work while they play.

The new IRS proposals also loosen up earlier, strict standards on tax deductions for offices in the home.

The rules make clear that a taxpayer can have a "principal place of business" for each business in which he or she is engaged. A high-school teacher who moonlights selling insurance from her home, for example, can set aside a separate office for that part-time business and take pro-rata deductions--including depreciation on the house--for that space.

Under the old IRS proposals, the teacher would have to make insurance sales her principal business--throwing her teaching career to the wind--if she wanted to take advantage of those tax writeoffs.