WASHINGTON — Frustrated by congressional gridlock, freshman Rep. Johnny Olszewski is proposing a constitutional amendment that would let voters enact federal laws directly, bypassing Congress on eligible issues. The Maryland Democrat plans to introduce the measure Thursday, Oct. 22. It would give supporters 18 months to gather signatures from at least 5% of voters who took part in the most recent presidential election in each of 25 states. A proposal meeting that threshold would go before voters at the next national election and need approval from 60% of the national vote. The initiative would not cover declarations of war or federal spending. Olszewski has pointed to proposals including a ban on congressional stock trading, police body cameras and protections for in vitro fertilization as examples of issues he says have public support but have stalled in Congress. “It’s been a long two years,” Olszewski said in an interview Tuesday. He said the dysfunction and missed opportunities he has seen as a new member convinced him that Americans need a way to act when lawmakers do not. The plan would make major changes to the federal lawmaking process, and the amendment itself faces formidable barriers: approval from two-thirds of both the House and Senate, followed by ratification from three-quarters of the states. Olszewski acknowledged that difficulty, saying he hopes the proposal will at least prompt a debate about congressional reform. A national ballot process would also raise practical questions about how measures are drafted, administered and applied across states. The 60% threshold is intended to require broad support, but it would still shift decisions now made through representative government to national campaigns and ballot fights. Olszewski, a former civics teacher, is pitching the proposal as a backstop rather than a replacement for Congress. “If we were acting, there’d be no need for this to come into play,” he said. The proposal comes as the 119th Congress has been described as among the least productive in modern history. Whether lawmakers will consider an amendment with such sweeping consequences remains uncertain.