WASHINGTON — After defending the Affordable Care Act in all its intricacies for six years, President Obama proposed ways to improve it on Monday, saying that Congress should provide larger subsidies for private health insurance and create a public plan like Medicare to compete with private insurers in some states.

At the same time, he accused the pharmaceutical industry of trying to protect its profits by opposing any constraints on drug prices.

Mr. Obama offered his views in a valedictory message summarizing what he sees as his legacy on health care, together with his ideas to improve the Affordable Care Act.

He said he was proud of the progress of the last six years, especially the fact that 20 million people had gained coverage because of the law. But he acknowledged that — despite the title of the law — health care and health insurance were still unaffordable for some people.