After months of political wrangling, Ukrainian lawmakers on Thursday passed a mobilization law aimed at replenishing the nation’s exhausted and depleted fighting forces, which are struggling to hold back relentless Russian assaults that are expected to intensify in coming months.

Yulia Paliychuk, a spokeswoman for the party of President Volodymyr Zelensky, confirmed that the law had been adopted by Parliament.

The urgent need for fresh troops has been evident since last fall, but Mr. Zelensky has been exceedingly cautious in dealing with the politically fraught topic, which has the potential to undermine the social cohesion that has played a critical role in Ukraine’s ability to wage war against a far larger and better-armed enemy.

Mr. Zelensky had urged lawmakers to act this week and is widely expected to sign the new legislation soon. However, the last time the Parliament passed controversial legislation related to mobilization — lowering the draft eligibility age to 25 from 27 last May — Mr. Zelensky waited nearly a year before signing it into law this month.

Mr. Zelensky was visiting Lithuania on Thursday.

The law passed by legislators on Thursday addresses the issue of mobilization more broadly, and includes provisions that lawmakers said were aimed at making the conscription process more transparent and equitable. The full text of the law was not immediately available.

But perhaps as important as what was included in the legislation is what was cut out — particularly a timeline for when conscripted soldiers will be demobilized.

Under martial law, which was imposed soon after Russia’s full-scale invasion of Ukraine in February 2022, conscripts are compelled to serve until the end of hostilities, with notably few exemptions. The original version of the bill submitted in February included provisions that would have capped mandatory service at 36 months.

But Gen. Oleksandr Syrskyi, Ukraine’s top military commander, urged lawmakers to separate the issue of mobilization from demobilization, a development first reported by the Ukrainian daily Ukrainska Pravda this week.

The removal of the provision to cap service at three years could provoke anger in the ranks, particularly among infantry soldiers who have been engaged in brutal combat on the front lines for more than two years with little respite.

Ukraine’s struggle to replenish its ranks comes as combat forces are struggling with shortages of ammunition and other critical supplies.

The U.S. Congress has not approved a new military aid package since October and a proposal that would provide a desperately needed infusion of $60 billion in military support has languished for months in the face of fierce resistance from a powerful faction of Republicans aligned with former President Donald J. Trump.

In contrast to Ukraine’s ammunition and personnel shortages, Russia has been able to sustain steep losses on the battlefield by recruiting an estimated 30,000 new soldiers to fight in Ukraine every month, according to Ukrainian intelligence officials and Western military analysts.

The British military intelligence agency said in a statement on Wednesday that the Kremlin was seeking to recruit 400,000 people in 2024 to sustain its forces in Ukraine.

Russia’s annual springtime conscription drive is expected to bring another 150,000 soldiers between the ages of 18 to 30 to its ranks who are less likely to serve in combat roles, the British agency said.

The mobilization issue in Ukraine has been a point of contention between Mr. Zelensky and some of his military commanders, who said last year that the nation would need as many as 500,000 new recruits of its own to counter the Russian threat. The rift was a key factor in the dismissal of Gen. Valery Zaluzhny from his post as the nation’s top commander.

Oleksandr Chubko contributed reporting.