WASHINGTON — The nation’s unemployment safety net is looking increasingly shaky, with a $300-a-week federal jobless benefit from the Trump administration running out just weeks after it began and millions of laid-off Americans nearing an end to their state unemployment aid.

Most Americans who exhaust their state’s unemployment benefits — typically after six months — will transition to an emergency federal program that provides an additional 13 weeks of aid. Yet they still face a looming deadline: By year’s end, nearly all the federal unemployment supports will expire. Unless Congress extends those programs, millions of jobless Americans could be cut off.

Their struggles come against the backdrop of an ailing job market with 13 million unemployed people and the pace of layoffs still elevated six months after the viral pandemic flattened the economy. Applications for unemployment benefits first spiked in the week of March 21, when they reached 3.3 million, then more than doubled the next week to a record 6.9 million. That means that anyone who began receiving state unemployment benefits then will have to shift to an emergency federal program in the coming weeks.

Separately, a spokesman for the Federal Emergency Management Agency, which is administering the $300-a-week federal benefit, said Thursday that the agency is providing money to cover six weeks, from the start of August through the end of this week, with no extension in sight.

Nearly all states have applied for the $300-a-week benefit. But only 17 have managed to upgrade their computer systems to actually distribute the payments. As a result, while many states will likely issue checks for several weeks, the money will be retroactive to early August and will cover only through mid-September.

Trump’s $300-a-week jobless aid program was created by an executive order last month after a more generous version adopted by Congress expired and Trump and Congress failed to reach agreement on a new aid package.

Through July, people out of work amid the coronavirus pandemic were receiving $600 a week in federal aid on top of their state unemployment benefits. For many recipients, the $600 federal check exceeded their state benefits and kept them afloat as the economy crumbled. But Republicans in Congress opposed the $600, arguing that it was so high as to discourage many of the unemployed from looking for a job.

On Thursday, Senate Democrats blocked legislation that would have extended the extra $300 payment and provided more money for schools. The Democrats favored restoring the full $600-a-week jobless benefit as well as more money for states, localities and small businesses.

Also Thursday, the Labor Department reported that applications for unemployment aid were unchanged last week at 884,000, and the number of laid-off workers who applied for aid under a separate program for the self-employed and contract workers increased. The figures indicated that companies are still cutting an unusually large number of jobs.