(FORTUNE Magazine) – MOST BUSINESS lobbyists cheered the idea of sweeping antitrust reform when President Reagan put forth his proposals on the subject in late February. But few of them were popping champagne corks once they got a close look at the five bills the Administration sent to Congress. It now looks as if the package could face insurmountable opposition when Congress takes it up. In addition to consumer groups and some business lobbies, the Administration will have to contend with New Jersey Democrat Peter Rodino, the chairman of the House Judiciary Committee and perhaps the most powerful man in Washington when it comes to legal legislation. Rodino attacks the package as ''a dismantling of antitrust laws'' and says it will not get out of his committee without drastic alterations. The centerpiece of the Reagan plan is a bill that would substantially weaken the Clayton Act of 1914, which prohibits mergers that lessen competition. Under Reagan, the Justice Department and the Federal Trade Commission have established the loosest guidelines ever for evaluating mergers. Now the Administration wants to write the guidelines into law so future Administrations will not be able to revert to tougher rules. Companies that fear being taken over are likely to fight that proposal. Takeover targets often use merger laws to shield themselves from raiders. Says Paul Lodato, a spokesman for the National Small Business Association: ''This further weakening of antitrust laws is a ploy to take over a lot of small companies.'' The second Reagan bill would meet a long-held goal of big business by doing away with triple damages for many antitrust violations. However, Reagan's plan is one business lobbyists are sure to oppose. In place of triple damages, the Administration would make defendants liable for interest on damages from the date a violation began. The object is to speed up lengthy antitrust litigation. Says Martin Connor, General Electric's Washington counsel: ''The interest requirement could offset any benefits gained by eliminating treble damages.'' A third bill would grant a five-year exemption from antitrust laws to industries that have taken a big hit from imports. Reaction to that idea has been negative, even from some companies it is supposed to help, because it carries a high price: in return for the freedom to merge for five years, industries would forgo quotas, tariffs, and other relief for the following ten years. ''It doesn't help us,'' says Fawn Evenson, a vice president of Footwear Industries of America. ''Our problem is high wages, not antitrust.'' Reagan's fourth bill is bound to draw the wrath of consumer groups. The Administration wants to water down a provision of the Clayton Act that prevents individuals from serving on the boards of certain competing companies. The final Administration bill would clarify the conditions under which U.S. companies can file antitrust suits against foreign competitors. Both business lobbyists and consumer groups say they can live with that piece of reform.