As long as Americans go around the world buying up companies and real estate, the U.S. can't reasonably expect to keep foreign investors from doing plenty of shopping on our own shores.

Indeed, since three-million Americans owe their jobs to foreign investment in the U.S., such outside ownership can considered a way to help the country grow.So there are sharp limits to how much Americans ought to be concerned over a new study this week from a private, non-partisan group called the Congressional Economic Leadership Institute, which reports that foreigners have more than tripled their investments in the U.S. since 1980.

What should concern Americans, however, is the fact that the U.S. puts fewer restrictions on outside investment than its own trading partners do, that the U.S. doesn't monitor foreign investment closely, and that consequently no one can be sure how much foreigners own and control firms essential to America's defense.

Though 16 different federal agencies keep track of foreign investment in the U.S., they don't always keep the same kind of records. Consequently, it's hard to compare those records from one agency to another. Moreover, the records are incomplete. They don't even distinguish the part-time and seasonal jobs created by foreign investment from the full-jobs.

Moreover, while the U.S. opens its arms to outside investment, other nations are much more meticulous about screening it not just to protect domestic industries but for the sake of national security.

This situation strongly suggests that Congress ought to reconsider the proposal it recently rejected to increase the monitoring of foreign investment. The proposal was rejected on the grounds that it would prompt other nations to respond in kind, but clearly they have beaten us to the punch. In any event, the new study scores a telling point when it notes:

"Britain, the Netherlands, Japan, Canada, and West Germany have concluded that all investments are not created equal. We ought to study their example carefully."