WASHINGTON — Senate Democrats today failed to restore lower interest rates on student loans, again coming up short and perhaps signaling that undergraduates might really face rates twice as high as the ones they enjoyed last year.

The proposal from Democratic leaders would have left interest rates on subsidized Stafford loans at 3.4 percent for another year while lawmakers took up a comprehensive overhaul. The one-year stopgap measure failed to overcome a procedural hurdle as Republicans — and a few Democrats — urged colleagues to consider a plan now that would link interest rates to the financial markets and reduce Congress’ role in setting students’ borrowing rates.

The competing proposals failed and lawmakers said students would face higher costs to repay their loans after graduation.

“Today our nation’s students once again wait in vain for relief,” said Sen. Tom Udall, D-N.M. “They expected more of us and I share their disappointment.”

The failure to win a one-year approval — combined with little interest in such a deal in the Republican-led House — meant students would be borrowing money for fall courses at a rate leaders in both parties called unacceptable.

The rate increase does not affect many students right away; loan documents are generally signed just before students return to campus, and few students returned to school over the July Fourth holiday. Existing loans were not affected, either.

However, absent congressional action in the coming weeks, the increase could spell an extra $2,600 for an average student returning to campus this fall, according to Congress’ Joint Economic Committee.