Senate Democrats are working to kill a Republican measure to slap sanctions on the Nord Stream 2 pipeline.

Senate Democrats unveiled legislation on Wednesday that would impose sanctions on top Russian officials if Moscow invaded Ukraine, in an effort to squash a competing Republican-led bill that would impose sanctions on a Russian natural-gas pipeline that bypasses Ukraine.

The Senate is expected to vote later this week on a measure led by Senator Ted Cruz, Republican of Texas, that would impose sanctions on Nord Stream 2, a Russian undersea pipeline to Germany viewed as a means of exerting influence over Europe. President Volodymyr Zelensky of Ukraine has both privately and publicly urged senators to support the bill, casting Nord Stream 2 as an existential threat. The pipeline would give Russia enormous leverage over Europe and would render Ukraine’s own pipeline to Poland obsolete, depriving Ukraine of substantial revenue.

But the Biden administration and its allies in Congress have lobbied against Mr. Cruz’s measure, which would go into effect 15 days after being signed into law, whether or not Russia attacks. They argue that quick passage would undermine unity among the nation’s European allies, including Germany, which has championed the pipeline as vital to its industrial success. They also argue that the sanctions would have little effect on the construction of the pipeline, because it is nearly completed.

They have instead encouraged Democrats wishing to penalize Russia for massing troops at Ukraine’s border to support legislation by Senator Robert Menendez, a New Jersey Democrat.

“We support Senator Menendez’s legislation, which would trigger severe costs to Russia’s economy and support additional security assistance to Ukraine should Russia further invade,” said Emily Horne, a spokeswoman for the National Security Council. “We will keep working with Congress on maximizing potential costs to Russia.”

That approach appeared to be resonating on Wednesday with even the most vocal Democratic defenders of Ukraine, as more than two dozen members of the party signed on to Mr. Menendez’s legislation. Ten Democrats would need to back Mr. Cruz’s bill in order for it to pass, and it would likely be doomed in the Democratic-controlled House.

“We need legislation that addresses the political situation we face today in response to increasing Russian aggression — not last year or two years ago,” said Senator Jeanne Shaheen, Democrat of New Hampshire. “The dynamics changed and so must our strategy.”

Mr. Menendez’s legislation would impose sanctions on top Russian officials, including President Vladimir V. Putin, as well as the nation’s banking sector if Russia engages in or supports “a significant escalation in hostilities or hostile action in or against Ukraine.” And it would provide Ukraine with $500 million in supplemental emergency security assistance in the event that Russia invades.

Republicans have argued that sanctions could still stop the completion of Nord Stream 2, and accused President Biden of indulging Russian lawlessness last year when the administration waived sanctions on the pipeline in an attempt to mend ties with Germany.

New sanctions on the Nord Stream 2 pipeline were included in the annual defense policy bill last year, but were quietly stripped out of the legislation at the last minute before its final passage.