TOKYO — The dollar, which tumbled to an almost 13-year low against the yen on Monday, may soon find a protector here — the Japanese finance ministry.

With broad powers over Japan’s nearly $5 trillion economy, the ministry has intervened in the past when the dollar fell sharply, notably late in 2003 and early in 2004 when it sold some $350 billion worth of yen to buy mostly dollars, propping up the value of the American currency.

A weak dollar hurts big Japanese exporters like Sony and Toyota by driving down the value of their overseas earnings in yen, and leading them to raise prices abroad to compensate.

Many economists and currency analysts are beginning to wonder whether the dollar’s sharp declines in recent weeks will push the ministry to try another large-scale intervention.

So far, it has chosen not to act, signaling a willingness to let market forces take their course. But if the dollar continues its drop, threatening Japan’s export-led economic growth, analysts say the government could come under increasing pressure to act.

“The ministry has shown itself very reluctant to intervene this time,” said Tohru Sasaki, chief foreign exchange strategist at JPMorgan Chase in Tokyo. “But the ministry may feel it has to do something” if the dollar continues to fall.

JPMorgan Chase’s agreement on Sunday to buy Bear Stearns rekindled uncertainty over the fate of American banks in the extremely tight credit market. On Monday, the dollar remained below parity of 100 yen, falling as low as 95.72 here during the trading session, its worst level since August 1995. In New York later, it settled at 98.04 yen. In the last month, the dollar has dropped more than 10 percent against the yen.

Concern for Japanese corporate profits, combined with fears of the effects of an American recession, drove the benchmark Nikkei 225 stock index down 3.7 percent on Monday, to a two-and-a-half-year low. Early Tuesday, the index was higher.

Over the weekend, articles in Japanese newspapers discussed when the finance ministry would be forced to step in and help to shore up the dollar. On Monday, Finance Minister Fukushiro Nukaga added to the speculation by calling the dollar’s recent declines “excessive,” signaling growing concern.

If the ministry does act, it will bring with it some of the world’s deepest pockets. During previous interventions in the currency markets, the ministry accumulated about $1 trillion worth of United States Treasury debt and other non-yen assets, helping give Japan foreign currency reserves second only to China’s.

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