President Reagan led his administration yesterday in attacking a Democratically sponsored trade bill that goes before the House today, saying the bill would punish the most productive farms and industries, not open markets for them.

"I'm dismayed at the protectionist legislation that is under consideration in the House," Reagan told a White House Rose Garden ceremony honoring leading American exporting companies. "It isn't a fair-trade bill. It is a less-trade bill. It will not open markets to U.S. products; it will close them."

White House spokesman Larry Speakes called the legislation "absolutely the worst bill . . . that could be possibly concocted" and said it is a strong candidate for a veto. He added that presidential aides found 18 major provisions "that we think would be absolutely disastrous to trade policy."

The president heard a recitation of six of them, Speakes continued, and said, "Stop. That's enough."

House Democrats, ordered by Speaker Thomas P. (Tip) O'Neill (D-Mass.) to have a comprehensive bill ready for floor action by mid-May, have rejected administration charges that it is protectionist.

"This bill doesn't deal with import restrictions. It deals with export promotion, making us more competitive in world markets," said Majority Leader Jim Wright (D-Tex.), who pulled the 458-page measure together from the contributions of seven committees.

The House bill is part of a bipartisan congressional push for tougher trade laws in the wake of record deficits, which reached $148.5 billion last year, and a growing frustration among proponents, who believe that the administration's actions against unfair trade practices have not gone far enough.

Sen. Lloyd Bentsen (D-Tex.), in his response Saturday to Reagan's weekly radio address, said the White House appears more concerned about protectionism in Congress than protectionism against U.S. industries by other countries.

Administration trade strategists acknowledged the House will likely pass the trade bill, but they are trying to cut down Republican support by painting it as a Democratic measure.

Although it comes with the full support of the Democratic leadership and key votes in the Ways and Means Committee split along party lines, portions of the bill sailed through other committees with large bipartisan majorities.

Minority Leader Robert Michel (R-Ill.), moreover, is sponsoring a Republican trade measure that contains provisions similar to ones in the Democratic bill.

In a speech before the National Press Club yesterday, U.S. Trade Representative Clayton Yeutter said it is "regrettable" that Democrats are trying to make trade a partisan political issue.