“THERE IS no Plan B.” So said Paul J. Wiedefeld, Metro’s low-key and usually understated general manager, who on Wednesday proposed what amounts to a last-ditch rescue package for a transit system that, though temporarily stabilized, stands at the edge of long-term financial and operational meltdown.

Having gone as far as he could with fare hikes, layoffs, service cuts and the SafeTrack maintenance surge, Mr. Wiedefeld has offered a plan for desperately needed new funding as well as structural changes — the most recent, and the most dire, wake-up call delivered to Metro’s federal and local stakeholders. For decades, they have answered such warnings by hitting the snooze button, willfully refusing to address structural problems that imperil not just the region’s subway and bus network, but also its prospects for growth, development and prosperity.

That is no longer an option. If the region and feds respond now by sticking their heads in the sand or delivering a quarter-loaf, the fallout will be worse than Mr. Wiedefeld’s departure — although that would be a likely result, and an unwelcome one. The real cost of inaction is the quickening erosion and bankruptcy of a $40 billion infrastructure network that has already been pushed to the brink: broken escalators; rickety rail cars and buses; mounting threats to safety; crumbling reliability; and the specter of even more passengers abandoning what was once the nation’s gold-standard subway system.

Mr. Wiedefeld’s blueprint is a blunt reminder that years of underinvestment have taken their toll. It calls for $15.5 billion in capital spending over a decade, nearly twice the current level, excluding borrowing — a bare-bones ask, whittled down from $25 billion in identified needs. To pay for that, he proposes $500 million annually in new, earmarked regional funding for long-term projects, as well as continued federal and regional investment at the current level of $300 million annually — all of it protected from raids for annual operations and maintenance. Metro’s regional partners would chip in an additional $26 million annually until the system built what would eventually be a $200 million rainy-day fund, a critical and now-missing asset used by major transit systems to cover unforeseen problems.

It all sounds ambitious, and it will be met with resistance by unions, which will dislike Mr. Wiedefeld’s plan to save money by outsourcing new projects, trimming retirement costs by establishing a 401(k)-style defined-contribution plan for new employees and, critically, reforming laws so that union demands for higher pay and benefits will not be greenlighted by arbitrators on the assumption that taxes will be raised to pay for them. The plan will get pushback from downstate lawmakers in Virginia, for whose constituents Metro is irrelevant, and perhaps also from Maryland Gov. Larry Hogan (R), who is skeptical of new transit spending — although opposing it in this instance may cost him dearly among suburban voters.

In fact, Mr. Wiedefeld’s approach is relatively modest, as notable for what is not included as for what is. He didn’t propose tearing up Metro’s compact, shrinking its board, submitting the system to federal control or ditching binding arbitration. Instead, he presented a measured, realistic and compelling case for bailing out a system in free fall. Here’s hoping the holders of Metro’s purse strings embrace the plan, before it’s too late.