Contributions to charitable organizations can now be claimed on tax returns only by those taxpayers who itemize deductions on Schedule A.

But for returns for the years 1982 through 1986, taxpayers who use the zero bracket amount instead of itemizing will be able to reduce their tax bills by a percentage of qualifying contributions made during the year.

The deduction will increase in steps over the five-year period. For 1982 and 1983, 25 percent of contributions up to a maximum of $100 may be claimed, for a top deduction of $25.

For 1984 the ceiling will jump to $300 while the rate stays at 25 percent, so the maximum deduction will be $75. In 1985 the percentage goes to 50 percent, and for 1986 up to 100 percent, with no dollar ceiling in either year (except for the normal limitation to 50 percent of adjusted gross income). The provision for this deduction expires after 1986.

This is not a "per-taxpayer" allowance. The percentage and ceiling figures will apply to all returns, with one exception. For a married person filing a separate return the dollar ceilings are cut in half, to $50 and $150, respectively, for those years in which ceilings apply.

This provision is intended as a tax incentive to encourage all taxpayers (including the majority who do not itemize) to contribute to charity. It is generally expected that private charities will be called on to pick up some of the load created by budget-mandated reductions in government assistance to the needy.

Home-sellers: A couple of present benefits for people who sell their homes are expanded under the new law, effective retroactively to July 20, 1981.

If you sell your residence, you now have 24 months (instead of 18 months) to buy a new home and be permitted to defer tax on any gain.

In addition, you get a six-month extension if you sold your home, haven't yet replaced it, and the original 18-month waiting period didn't expire until July 20, 1981 or later.

The one-time exclusion of gain for home-sellers age 55 or older is increased from $100,000 to $125,000 for sales made after July 20, 1981. All the qualifying requirements remain unchanged.

Employes abroad: U.S. taxpayers living and working abroad get a major improvement in the amount of income that can be excluded from tax, beginning Jan. 1, 1982.

The rules can get to be fairly complicated. Anyone in this category should read them carefully, and may want to get professional help. Here's a quick review of the major elements:

Required time in-country changes. To qualify for tax exclusion you must be a bona fide resident of a foreign country (or countries) for an uninterrupted period which includes an entire tax year, and be physically present there at least 330 full days during any 12-month period.

If you qualify, you'll be able to exclude up to $75,000 of foreign earned income in 1982. This amount will increase by $5,000 each succeeding year until it levels off at $95,000 in 1986 and later years.

In addition, you will be permitted to deduct "reasonable housing expenses" to the extent that they exceed 16 percent of the salary of a civil service employe in step one of grade GS-14.

If you are required to maintain separate housing elsewhere (but still outside the United States) for your family because of adverse living conditions at your assigned location, then you can include housing expenses at both places in the computation.

Miscellaneous: Several minor items were included in this omnibus tax bill, including the following:

Congress has imposed a further hold until Dec. 31, 1983, on any action by the IRS to tax fringe benefits.

The 1 percent excise tax on telephone services is extended two years, until Jan. 1, 1985.

An estimated tax return has been required if you anticipated that your tax liability would exceed the amount to be withheld from your pay by $100 or more. That floor is raised by $100 each year until it reaches $500 for 1985 and succeeding years.

The rules governing commodity straddles have been tightened. This is a highly technical area; one of the more significant effects will be to prevent most taxpayers from applying losses from incomplete straddle transactions to offset income from other sources.

And still to come next week: Changes in the rules governing IRA and Keogh retirement plans; and a quick look at major changes in estate and gift tax regulations.