WASHINGTON – President Barack Obama will deliver a major address to Congress next Wednesday, confronting critics of his health care overhaul and trying to buck up supporters on an issue that has been slipping from his control under withering Republican-led attacks.

The speech will underscore an acceleration of Obama’s direct involvement in proposals to overhaul the nation’s health care system. Many allies have been urging him to be more specific about his plans and to take a greater role in the debate, and White House aides have signaled he will do that in the address to a joint session of lawmakers in the House chamber.

The speech’s timing suggests that top Democrats have all but given up hope for a bipartisan breakthrough by Senate Finance Committee negotiators. The White House had given those six lawmakers until Sept. 15 to draft a plan, but next week’s speech comes well ahead of that deadline.

It will come a day after lawmakers return from an August recess in which critics of Obama’s health proposals dominated many public forums. Approval ratings for Obama, and for his health care proposals, dropped during August.

Senior adviser David Axelrod had said Tuesday that Obama was considering being “more prescriptive” about what he feels Congress must include in a health bill.