Chemical manufacturers took an unexpected dousing yesterday as the House defeated a series of pro-industry amendments and then approved a two-year extension of the basic federal pesticide control law.

Final vote on extension of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) was 352 to 56, although that did not reflect the intense behind-the-scenes lobbying over the bill in recent days.

Heavy industry lobbying, although sufficient to force the Reagan administration to change position on two key issues, wasn't enough to undo the chemical horror stories that unfolded on the floor yesterday.

There were reports of herbicide poisoning of national forests in Oregon, of Hawaiian milk contaminated by a pineapple-crop chemical and of water on Long Island tainted by a potato growers' chemical. There was worry about fire ant-infested southern suburbs being sprayed with a carcinogenic chemical.

Rep. Sidney R. Yates (D-Ill.) told of newly discovered cancer in his wife and his concern that atmospheric drift of toxic pesticides from state to state could harm public health.

After that, Yates easily won approval of a ban on toxaphene, a cotton chemical acknowledged by the Environmental Protection Agency to cause cancer in humans.

EPA has studied the chemical for months but not acted against it, Yates reported, although its toxicity was well known.

Even at that, the FIFRA bill the House tinkered with yesterday was "quite beneficial to the chemical industry," said Rep. George E. Brown Jr. (D-Calif.), whose Agriculture subcommittee produced the legislation.

Before the House completed work, it took the unusual step of rebuffing the main authorizing committee on a number of major sections that were dear to the chemical industry.

For example:

The most controversial section, concerning states' powers to be more restrictive on pesticides than the federal government, resulted in a defeat for the committee.

An amendment by Rep. Tom Harkin (D-Iowa), erasing new limits on the states and retaining present law, was adopted 250 to 154. Harkin's amendment was supported by most farm groups, by governors, state agriculture directors and environmentalists. Chemical manufacturers, the administration and the American Farm Bureau were the chief opponents.

An amendment by Rep. Leon E. Panetta (D-Calif.) to allow private citizens access to federal courts to seek relief from pesticide damage was adopted by voice vote. A number of members complained that it didn't go far enough.

The committee bill provided only access to state courts for private citizens, but it gave corporations access to federal courts and called for treble damages in certain litigation. Earlier, an effort by Rep. William M. Thomas (R-Calif.) to limit the Panetta amendment was rejected on a voice vote.

Rep. Elliott H. Levitas (D-Ga.) argued for an amendment to assure access of scientists to manufacturers' formulation data to determine the health and safety effects of new products.

When Levitas appeared near success, Brown huddled outside the chamber with lobbyists from the National Agricultural Chemicals Association and decided to beat a hasty retreat.

Brown offered to remove from the bill the restrictive section that Levitas was trying to crack open.

Rep. James Weaver (D-Ore.), a member of the Agriculture Committee, was as surprised as the rest of the House at the unexpected turn of the day's events. "I've sat here today amazed," he told the House. "I would have offered stronger amendments in committee, but I didn't think they would be acceptable to the committee or the country . . . . I'm beginning to believe we've underestimated what's happening here."