No such outcry has greeted the purchase of stakes in major Wall Street banks by state investment funds in the United Arab Emirates, Kuwait, China, Singapore and South Korea. This is largely because the banks sold passive slices and ceded no formal control, which would have set off a federal review of the national security implications. But the silence also reflects the imperative that these enormous institutions swiftly secure cash.

“It would be good if these companies didn’t need all this capital and better if the capital was available in the United States,” said Senator Charles E. Schumer, Democrat of New York, who was a vocal opponent of the DP World deal. “But given the situation that these institutions find themselves in and the fact that there’s a pretty strong credit squeeze, there’s only two choices: Have foreign companies invest in these firms or have massive layoffs.”

In years past, particularly when Japanese money washed in, many foreign purchases proved not to be so prudent in the end. This time, with the dollar weak and troubled American companies in a poor bargaining position, the prices really do seem cheap, some economists say.

“They’re buying financial assets at well under book value,” said Gary C. Hufbauer, a trade expert at the Peterson Institute for International Economics.

Trade experts assume tensions will rise as developing countries — which tend to have more state companies — continue to expand their share of investment in the United States.

Canada still spends the most money buying stakes in American companies — more than $65 billion in 2007, according to Thomson. But other countries’ purchases are growing rapidly. South Korea’s investments swelled to more than $10.4 billion last year from just $5.4 million in 2000. Russia went to $572 million from $60 million in that span; India to $3.3 billion from $364 million.

But even if political tension increases, so will the flow of foreign money, some analysts say, for the simple reason that businesses need it.

“The forces sucking in this capital are much bigger than the political forces,” said Mr. Garten, the Yale trade expert. “If there is a big controversy, it will be between Washington on the one hand and corporate America on the other. In that contest, the financiers and the businessmen are going to win, as they always do.”