Secretary of State George P. Shultz's demand this week that South Korea honor trade agreements aimed at opening certain Korean markets to American goods was made in unusually blunt language.

It may have been intended as a signal to other Asian countries, and possibly the world, that open trade must be practiced on both sides if U.S. trade protectionism is to be avoided.If that is the intent of the Shultz warning, it is long overdue. The U.S. cannot continue to allow other countries to sell in America while keeping their own doors closed to U.S. goods.

Since World War II, the U.S. has played a key role in helping many nations rebuild their economies and make improvements that have raised their standard of living. The success of those efforts is widely evident in the introduction of high-quality imports, especially electronic items and automobiles, to U.S. markets.

But now, with the U.S. economy struggling and American industry needing both physical and financial renewal, it is time for reciprocal treatment from those who have benefited.

Shultz gave clear warning to South Korea that the U.S. intends to continue pressure on Korea to drop trade barriers, despite any anti-American feelings it may provoke.

South Korea recorded a $10 billion trade surplus with the United States last year and, as a result, U.S. officials believe it is time to remove trade barriers that prevent American companies from penetrating South Korean markets.

Similar trade imbalances are building with other countries, most notably Japan. These imbalances must be reduced if the United States ever hopes to rein in its growing national debt and reduce or eliminate its troublesome budget deficit.

While the warning shot was fired in South Korea, it is important that Americans at home listen carefully as well. Opening foreign markets is just the first step. That must be followed by quality American-made products at prices competitive with domestically produced items.

All the trade freedom in the world will not cut the trade imbalance if the product will not sell.

If foreign trade doors are to open, it is imperative that Washington resist calls for protectionist legislation. It is incumbent on the U.S. to prove itself in the world market by providing quality goods at competitive prices.