House Democrats yesterday unveiled a comprehensive trade bill that they said would improve America's competitive position in the world, but President Reagan immediately called on Republican lawmakers to work against it.

"They try to make it sound like an 'act tough' policy, but it's really a tough-luck policy for U.S. taxpayers, consumers and exporters," White House spokesman Larry Speakes quoted the president as telling Republican congressional leaders.

The 458-page bill, which calls for a tougher response to other countries' unfair trade practices and adjustment assistance and educational opportunities for workers hurt by surging imports, is due to go to the House floor next Tuesday. It has the full support of the Democratic leadership, which took pains to deny charges that the legislation is politically motivated and pushes protectionism.

The bill got its partisan Democratic label because House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) set its timetable, and the Ways and Means Committee voted on party lines to approve one of its major portions and to kill a Republican substitute drafted by Minority Leader Robert H. Michel (R-Ill.).

But Majority Leader James C. Wright Jr. (D-Tex.) said key portions of the bill received heavy bipartisan support when they were considered by the Energy and Commerce and Foreign Affairs committees.

He also dismissed the protectionist label used by the administration and some business interests to describe the Democratic bill. "It doesn't deal in import restrictions," Wright said. "It deals with export promotion, making us more competitive in world markets."

"The foreigners are skinning us alive with unfair trade practices. This legislation brings them to a halt without engaging in protectionism," added Chairman John Dingell (D-Mich.) of the Energy and Commerce Committee.

As an indication of the widespread support the bill has from House Democrats, Rep. Sam Gibbons (D-Fla.), a long-time advocate of free trade, joined in favoring the bill. In the past, he led the opposition to other major trade bills, including a Dingell-sponsored measure to require foreign cars to have a large made-in America component, because he said they were protectionist.

President Reagan's statement to Republican legislators yesterday was the opening salvo in an administration campaign to defeat the House bill, which he said "would result in less trade overall and higher costs to the consumer and the taxpayer."

"The Democrats' response to the trade deficit is to redistribute a shrinking pie rather than stimulate new growth and opportunity for expansion," the president was quoted as telling the GOP congressional leaders.

In a statement at a Senate hearing, Treasury Secretary James A. Baker III warned Congress against protectionist bills that could worsen the trade deficit.

"We must avoid passage of protectionist trade legislation that would alienate our trading partners, encourage them to enact similar protectionist policies and undermine the administration's international economic policy," he said.

But Sen. John C. Danforth (R-Mo.), who is pressing for a tough Senate trade bill, accused the Reagan administration of "defining anything that walks as protectionist.