Sen. Tom Harkin (D-Iowa) was in Washington yesterday, far from his home-state campaign trail, but 50 of his Democratic colleagues got together on the floor of the Senate to help along his reelection bid.

The 50 Democrats, plus Harkin and Iowa's other senator, Republican Charles E. Grassley, prevented the Senate from debating a provision in an appropriations bill to establish a foreign trade zone in Cedar Rapids. As a result, the provision stayed in the bill.

The 52 to 47 vote blocking debate on the provision reflected the partisan subcurrents swirling around final action on the 13 appropriations bills as Congress moves simultaneously toward adjournment and the Nov. 6 election.

Late Tuesday night a partisan impasse threatening another measure, the $15 billion foreign aid spending bill for fiscal 1991, was resolved, permitting the Senate to complete action.

Antiabortion forces had threatened a filibuster if Sen. Timothy E. Wirth (D-Colo.) went ahead with plans to try to overturn a longstanding U.S. ban on aid to international organizations that dispense information about abortion.

In a retaliatory tactic, Sen. Jesse Helms (R-N.C.), an abortion opponent, had also threatened to force the Senate to vote on an amendment to use a 29 percent cut in the bill as a substitute for the gas tax increase being discussed by budget negotiators.

In bargaining this week, Helms and Wirth agreed to drop their amendments, clearing the way for yesterday's 76 to 23 Senate passage of the aid bill. It now goes to a conference with the House.

The Senate bill would forgive Egypt's $7 billion military aid debt, a major administration foreign policy goal. But the House-passed version contains no such provision, which could give the House conferees leverage with the administration in preventing a veto of its cuts in aid to El Salvador.

The foreign trade zone vote came as the Senate approved a conference report on 1991 appropriations for the Commerce, Justice and State departments.

Cedar Rapids' foreign trade zone designation was inserted in the bill during a House-Senate conference by Rep. Neal Smith (D-Iowa), who chairs the appropriations subcommittee that drafted the measure.

The special status would allow local Cedar Rapids manufacturers to import foreign parts and material duty free and reexport them. Among beneficiaries is the U.S. subsidiary of South Korea's Poongsan Metal Corp.

The proliferation of free trade zones was the subject of hearings in the House this year and is a matter of growing concern to domestic steel and other manufacturing industries, according to a spokesman for Sen. John Heinz (R-Pa.), who introduced the amendment that would have stricken the Cedar Rapids zone from the bill.

David Hartquist, an attorney specializing in trade, called the Cedar Rapids provision "a total circumvention of the process that's normally followed" in trade cases.

Poongsan Metal was among foreign companies targeted in an anti-dumping suit filed in 1986 by the U.S. copper and brass industry. The Commerce Department and International Trade Commission upheld the complaint and required Poongsan to pay a 7 percent duty.

The establishment of the free trade zone could exempt Poongsan from paying the duty if its products were reexported, according to sources.

Harkin and Grassley are members of the Senate Appropriations Committee; Harkin chairs the subcommittee that allocates more than $50 billion annually to education and health programs.

The appropriations role has been an asset in his close reelection contest against Rep. Thomas J. Tauke (R-Iowa), enabling Harkin to claim credit for expansion of funding for aging and youth programs popular in his home state.

He also has had a helping hand from appropriations colleagues. The interior appropriations bill, for example, contains a $1.2 million grant to the University of Northern Iowa in Cedar Falls for a regional metals casting center.