Six major business organizations, joining yesterday to urge the Reagan administration and Congress to approve "constructive" trade legislation this year, set out the parts of bills now in a House-Senate conference that they support and sections they find unacceptable.

The joint statement by the six organizations is aimed at increasing the influence of business in the ticklish job of crafting trade legislation from different bills passed by the House and Senate and persuading President Reagan to sign it even if it contains some provisions he does not fully support.

The six organizations are the Business Roundtable, Emergency Committee for American Trade (ECAT), National Association of Manufacturers, National Foreign Trade Council, U.S. Chamber of Commerce and the U.S. Council for International Business. They represent "the mainstream of U.S. business," said Robert McNeill of ECAT, who spoke for the newly formed Business Coalition on Trade.

The statement came as Congress was struggling with the organization of one of the largest and most complex conferences ever attempted. The conference will include 199 lawmakers who will try to develop one piece of legislation from the separate bills, each 1,000 pages long.

Representatives of the business groups said the odds favor passage of a bill this year.

The business coalition endorsed six major provisions of the bill: granting authority for the president to conduct global trade negotiations; changing the Foreign Corrupt Practices Act; improving protection for intellectual property; streamlining export control laws; forcing stronger action against countries that violate trade agreements, and improving the law giving relief to industries hurt by a surge of imports.

The business groups split on one of the most controversial issues, whether the president should be forced to grant relief if the International Trade Commission finds that an industry has suffered harm from imports.

The measures the groups opposed were: a requirement that big businesses give workers advance notice on plant closings and mass layoffs; a provision sponsored by Rep. Richard Gephardt (D-Mo.) to force countries to cut "excessive" trade surpluses or face retaliation; the use of a tax on imports to finance help for workers laid off because of foreign competition; registration requirements for foreign investment; restrictions on World Bank and International Monetary Fund loans, and new definitions of unfair trade practices.