The change in the tax code that prohibits the use of collectibles such as antiques, gold and diamonds as the basis for tax-deferred individual retirement income accounts has caused a mixed reaction among dealers. Those interviewed who specialize in coins, gems and stamps believe the ban will affect them substantially, but those dealing in fine arts predict a negligible effect on their business.

That one sentence in the tax bill recently passed by Congress may cost fine arts and metals dealers hundreds of millions of collars in lost sales, said Michael Freedman, president of Gemstone Trading Corp., a New York diamond broker. Freedman called the change "outrageous" and said he and other dealers plan a "vigorous resistance" against what they see as "a blatant grab by the banking industry to prevent investors from determining where they'd like to put their funds. It's a negative response to [the industry's] inadequacies," he added.

Writer and lecturer Howard J. Ruff, who favors investing in collectibles---especially gold, yesterday announced the start of a national lobbying campaign to get the prohibition against collectibles repealed. He declared, "This administration and Congress have biolated a free-market principle that has nothing to do with tax-cutting."

The provision that Freedman and Ruff oppose was added to the bill at the last minute at the request of the savings industry. The Ways and Means Committee report issued when it passed the bill cited concern "that collectibles divert retirement savings from thifts and other traditional investment media and that investments in collectibles do not contribute to productive capital formation."

The Employment Retirement Income Security Act of 1974 created the Individual Retirement Account without stipulating which investments would be acceptable for tax deferral. The boom in collectibles began a couple years later when the dollar sank on international markets and some Americans put their faith in tangible items rather than paper money.

Statistics compiled by Salomon Brothers bore witness to the appreciation of collectibles: Over a five-year period, gold averaged a 31 percent annual increase; Oriental rugs, 21 percent; U.S. coins, 30 percent; and diamonds, outperformed stocks, which gained just 9.8 percent, and bonds, which rose 1.1 percent in the same period.

But then last year the speculative bubble in art and metals investments burst, pricked by high interest rates, by a strengthening dollar and stock market, and by high-yielding money market funds. Precious metals, coins, diamonds and Oriental rugs -- the most popular tangible investments among professional investors -- suffered the most. Gold was down 14 percent; silver, 27 percent; coins, 8 percent; and rugs, 0.2 percent. Diamonds registered no net gain, but that figure masks wild highs and lows in trading throughout the year. And the outlook is not terribly bright, according to Collector Investor magazine.

The latest available figures from the Internal Revenue Service put the amount contributed to IRA and KEOGH accounts at $5.2 billion in 1979. Two years earlier the IRS did a breakdown of IRA portfolios and found that just 2.7 percent of the investments were listed in the "other" (than bank accounts, stocks, bonds, annuities) category. Some portion of this was invested in collectibes.

Rafael Guber of the New England Rare Coin Galleries in Boston estimated that less than 5 percent of his company's total sales were for IRA and Keogh accounts.

By contrast, Steven Lash of Christie's, a New York auction house, applauded the change. "We have never felt that art as an investment was a very good idea," he said.