Defying Republican leaders, the House voted on Wednesday to take up a bill to impose sweeping new sanctions on Russia and provide additional aid to Ukraine, after a bloc of G.O.P. defectors joined Democrats in an effort to ratchet up pressure on Moscow more than four years into the war.

The bill, which still must win passage in the House, faces a difficult path to enactment, given divisions in the Senate over a sanctions package and objections from the White House. President Trump has repeatedly signaled he does not want Congress constraining his flexibility to negotiate directly with Moscow, and could veto the legislation if it reaches his desk.

Still, the 218-to-204 vote to take it up, in which six Republicans and one independent who normally votes with them crossed party lines to side with Democrats, sent a clear signal of bipartisan pressure on the matter. It added to growing a list of issues on which the Republican-led Congress has in recent weeks shown a greater willingness to challenge Mr. Trump, including the war with Iran, his push to fund a new White House ballroom and a bid to create a federal fund to benefit his political allies.

The legislation’s centerpiece is a broad package of sanctions targeting Russia’s oil and gas sector that is aimed at striking at the Kremlin’s primary source of wartime revenue. Lawmakers in both parties have argued for more than a year that sanctions imposed by the United States and its allies have failed to fully sever the energy revenues that continue to bankroll Moscow’s war effort.

The bill would expand restrictions on financial institutions that conduct business with sanctioned Russian officials and state enterprises and seek to crack down on entities that help Moscow evade existing sanctions. It also would target international organizations, companies, banks and governments that continue doing business with sanctioned Russian entities, provisions primarily aimed at actors in China, Central Asia and other jurisdictions that have helped Russia circumvent Western restrictions.

And the legislation would eliminate a sanctions waiver President Trump approved earlier this year that provided limited relief.

It would authorize roughly $1.8 billion in direct spending and more than $8 billion in loans for Ukraine’s war effort as the country continues to face deadly bombardment in Kyiv and other areas.

The bill languished for more than a year as Republican leaders on the House Foreign Affairs Committee declined to take it up, preventing lawmakers from debating and amending it.

That prompted Representative Gregory W. Meeks of New York, the committee’s top Democrat, to turn to a procedural maneuver known as a discharge petition, which allows rank-and-file lawmakers to bypass the leadership and force a bill to the House floor if it gains the support of a majority of members.

It took more than a year to gather the required signatures, a threshold that was reached last month when Representative Kevin Kiley of California, an independent who caucuses with Republicans, joined G.O.P. Representatives Don Bacon of Nebraska and Brian Fitzpatrick of Pennsylvania, in breaking with party leaders and backing the effort.

On Wednesday, four additional Republicans — Representatives Mike Lawler of New York, Michael McCaul of Texas, Max Miller of Ohio and Joe Wilson of South Carolina — joined Democrats in voting to move ahead with the measure.