A critical federal subsidy for Metro would increase to $200 million a year on condition that the agency adopt new oversight and safety measures, under legislation the region’s senators plan to introduce.

The long-awaited Senate proposal would extend the decade-old federal funding program that has provided the transit agency with $150 million a year for another 10 years. In addition to increasing the annual funding by $50 million a year, the legislation also strengthens the office of Metro’s inspector general, tightens procedures for capital spending, and creates two task forces to improve safety on Metrorail and Metrobus.

A draft of the bill, a copy of which was obtained by The Washington Post, was hammered out over months in talks with Metro, government leaders and other stakeholders, including key senators from outside the region. It is being circulated for final comment before being filed.

The legislation is viewed as a promising vehicle for winning long-term continuation of the federal subsidy that has been a vital part of Metro’s capital budget for purchasing rail cars, buses and other equipment.

Congressional staffers and others familiar with the bill said they were optimistic that it would pass this year. They noted that Metro has enjoyed bipartisan support and that the system plays an important role in transporting the federal workforce.

Some of the proposed changes were designed in part to win support from Republicans in the GOP-controlled Senate, including ensuring the independence of the inspector general and guaranteeing funding for the office, and requiring more rigorous planning for capital spending.

The bill also strongly advises the Metro board to continue to limit the role of its alternate members — a practice that was started last year as a way to streamline the panel and improve its effectiveness. The board has eight voting members and eight alternates.

As previously reported, the planned bill would block the federal subsidy altogether if Metro buys its next generation of rail cars from the state-owned China Railway Rolling Stock Corp. The firm’s penetration of the U.S. transit car market has raised concerns in Congress, the Pentagon and elsewhere that it will dominate the sector and possibly provide a platform for cyberespionage.

Metro typically does not like conditions placed on its funding, but the agency did not mention any concerns in a brief statement welcoming the proposed legislation.

“We are especially grateful to our senators and the entire Congressional delegation for supporting funding for Metro and taking this important step toward continued investment in safety and reliability improvements,” spokesman Dan Stessel said.

The 10-year federal subsidy for Metro was created as part of the 2008 Passenger Rail Investment and Improvement Act, or PRIIA. The program expired in October, and Metro recently received its last allocation of funding authorized under the act.

Democratic Sens. Mark R. Warner and Tim Kaine of Virginia, and Chris Van Hollen and Ben Cardin of Maryland have been laboring to draft a bill to extend the subsidy.

The legislation would extend the $150 million annual authorization through 2029 without new conditions. As before, Metro would get the money only if the District, Maryland and Virginia each contribute $50 million a year in matching funding. Even with the authorization in place, the money must be appropriated by Congress each year.

Of the additional $50 million a year proposed in the bill, $45 million would be for capital spending and preventive maintenance projects. The money would be conditional on the reforms but would not have to be matched by the jurisdictions.

The remaining $5 million of new funding would go to the office of the inspector general and would have to be matched by nonfederal funds from Metro’s budget, raising the total for the office to $10 million a year.

Congress ordered the creation of the inspector general’s office as part of the PRIIA to provide extra oversight of Metro for the sake of safety, fiscal responsibility and customer service. Partly because of congressional support, Inspector General Geoff Cherrington has seen his budget nearly double, to $9.8 million, since he took office two years ago.

“I think Congress just wants to ensure that the $10 million is consistent and can’t be taken away,” Cherrington said of the draft legislation.

The proposed reforms to the agency’s capital spending process reflect recommendations from the Government Accountability Office in a January report.

The proposal for two task ­forces originated in a House bill proposed in the previous congressional session by Reps. Jamie B. Raskin and Anthony G. Brown, both Maryland Democrats.

The task forces have the support of Metro’s largest union, Amalgamated Transit Union Local 689, and are named for two Metro workers who died on the job: Jeanice McMillan, the train operator who was killed in the 2009 Red Line crash near the Fort Totten station, and Thomasine Maria Smith, a bus driver who was killed in a 2013 crash in Silver Spring.

Both task forces would review Metro’s safety programs for on-track rail and bus service, and make recommendations for improvements.