This year, the 20th anniversary of the Exxon Valdez oil spill, would be an appropriate time for Congress to affirm in law one of the key safety measures designed to prevent another such disaster.

Each time an oil-laden tanker passes through Prince William Sound, it is escorted by two massive tugboats. Federal law requires that two such tugs accompany tankers with single hulls but not tankers with double hulls.

The dual escorts should be required for all tankers, and Congress should make it happen as soon as possible.

The Alaska tanker fleet has gradually converted to double hulls, in accordance with federal law passed after the spill. The final single-hulled tanker, in fact, should retire by 2012.

Even as oil companies have phased in the double-hulled tankers, they have retained the dual escorts for each. It's a wise policy but one that could be dropped too easily after the last single-hulled tanker leaves. Congress should not present the opportunity.

Double hulls are worthwhile, but they still represent thin protection against a spill if a tanker hits a rock, dock or ship. The lower standard of caution is not justifiable.

A fully laden tanker needs two escort vessels to ensure complete control when the tankers' main engines go down, especially if winds or currents are strong and obstacles are near.

This is not a theoretical risk. Tankers have lost power infrequently but regularly during the past two decades.

Legislation that would require two escort tugs for all oil-laden tankers passed in the U.S House. Rep. Don Young inserted the two-escort rule in the Coast Guard's authorization bill.

Progress in the Senate is less clear. Sens. Lisa Murkowski and Mark Begich have introduced a freestanding bill to require dual escorts, but the provision has not yet appeared in the Senate's Coast Guard bill. It doesn't need to be there, as long as the provision in the House version stands.

This is the right year for Congress to do the right thing and require that two tugs escort all outbound tankers in Prince William Sound.