THE ability of Hong Kong groups to cut US withholding taxes by investing in the US through companies registered in the Netherlands will be ''severely curtailed'' from January 1, 1995, says Hong Kong American Chamber of Commerce taxation committee chairmanRichard Weisman. He said companies now used Netherlands holding companies to own shares in their US subsidiaries, to lend to them and in some cases license intellectual property rights to the subsidiaries. The ratification of the new US-Netherlands tax treaty this week came just days before the effective date of the treaty would have been pushed back another year. ''The significance of the new treaty for these companies is that many will no longer qualify for the benefits of the tax treaty, principally reduced withholding taxes,'' Mr Weisman said. Mr Weisman, who is an American lawyer with the international tax group at Baker & McKenzie in Hong Kong, said although the nominal effective date of the new treaty would now be January 1, 1994, Hong Kong groups which had qualified for greater benefits under the old treaty would be able to continue to benefit from the old treaty for another year. These Hong Kong groups should now focus on whether they could structure their international operations to qualify for certain exemptions to the treaty's new limitation of benefits provisions, Mr Weisman said. He cited as examples exceptions for so-called qualified headquarters companies, for ''active trade or business'' relationships between the Netherlands and US companies, and the exception for certain publicly listed companies.