One of the most important battles of the Indochina war appears to be developing in southern Laos.

Sources near the Laotian panhandle reported yesterday that the South Vietnamese military command is dispatching 16,000 troops to Laos to bolster Allied forces already engaging North Vietnamese units.

Lt. Gen. James W. Sutherland, commander of American forces in Laos, said yesterday that the North Vietnamese appear to be marshalling all their forces to thwart the U.S.-backed invasion of Laos.

Sutherland said that the Allied drive into Laos has proceeded slower than intended but argued that the offensive has been successful in blocking the movement of North Vietnamese supplies.

"The enemy has chosen to react with everything he's got left so it appears we'll have to fight him right here," Sutherland said.

In the Senate, J.W. Fulbright (DArk.), chairman of the Senate Foreign Relations Committee, told reporters that he has asked the State Department for the second time to supply details of South Vietnamese plans to grant offshore oil concessions to American companies.

Fulbright sent his second letter to the State Department after he found an initial department reply unsatisfactory.

Although no oil has yet been found off Vietnam. U.S. companies have expressed an interest in bidding for the off shore leases. Bids originally were scheduled for February, but Mobil and Gulf asked the South Vietnamese government for a 60-day postponement until proposed South Vietnamese legislation concerning the offshore oil leases is clarified.

Elsewhere, a Senate panel yesterday praised the Pentagon's $1.6 billion sensors program in Indochina, saying it saves U.S. lives.