WASHINGTON  The Obama administration increased its criticism of China’s economic policies on Thursday, as Treasury Secretary Timothy F. Geithner told Congress that China had substantially undervalued its currency to gain an unfair trade advantage, tolerated theft of foreign technology and created unreasonable barriers to American imports.

But the election year anger from lawmakers seemed to surpass even Mr. Geithner’s tougher posture. Lawmakers expressed impatience with the administration’s familiar reliance on persuasion and negotiation, saying such tactics had yielded little.

In Beijing, a spokeswoman for the Foreign Ministry said that China would not respond to pressure and that a revaluation of the currency, the renminbi, would do little to affect the United States trade deficit with China. But the renminbi strengthened by 0.27 percent to end trading at 6.72 per dollar Thursday as the government appeared to belatedly permit the greater currency flexibility it had promised in June.

Dismay over China’s currency interventions  it buys about $1 billion a day to maintain the renminbi’s peg to the dollar  has been a recurring theme for years. The election-season rhetoric, the carefully calibrated strengthening of the Chinese currency on the eve of Mr. Geithner’s appearance, and the administration’s struggle to negotiate a diplomatic line set the stage for predictable political theater.