Washington ? With only four legislative weeks left, congressional Republicans and Democrats have defined their positions on most key issues in the Nov. 7 elections, staking their political fortunes on sharply different views about Iraq, immigration, taxes and stem cell research.

Both parties are still honing their messages, but the outlines came into focus late this week as Congress wrapped up its work for the summer. Local issues will play important roles in some House races, but polls suggest the election will largely be a national referendum on President Bush’s performance, especially the war in Iraq.

After privately debating the war for months, congressional Democrats coalesced this week around a call to begin withdrawing U.S. troops this year. Republicans have concluded they have little choice but to stand by the president by supporting his war policies and resisting a timetable for withdrawing troops.

The impasse in the Senate last week ensures that tax and minimum-wage policies will play a big role in many campaigns this fall. Democrats blocked a GOP bid to link a deep and permanent cut in the estate tax – which would benefit the wealthiest Americans – with an increase in the federal minimum wage, which would help the working poor.

Immigration is a trickier matter, because the key impasse involves House Republicans on one side and Senate Republican leaders and Bush on the other. House Republicans have vowed to crack down on illegal immigration before taking any other steps. Solid majorities of Democrats favor a more comprehensive approach, as do the president and a minority of GOP senators. They would include a guest-worker program and means for some illegal immigrants to gain legal status.

The stem cell issue also is vexing for Republicans. Most House and Senate GOP lawmakers support increasing federal financing of embryonic stem cell research, but Bush used his first veto last month to reject it. Democrats in key races are portraying Republicans as beholden to a far-right constituency, and Bush’s veto complicates the efforts of pro-research Republicans to defend themselves and their party.