SAIGON — America's top military leaders sloshed through muddy remote villages of the strife-torn Republic of Vietnam to learn first-hand how the war against the Viet Cong is going.

Defense Secretary Robert S. McNamara and General Maxwell D. Taylor, chairman, Joint Chiefs of Staff, spent several dawn-to-dusk days talking with American and Vietnamese military officials. They spoke with Vietnamese villagers, Montagnards and even with captured Viet Cong rebels.

Several times they boarded a helicopter to visit forward command post positions.

During their tour, McNamara and Taylor visited a Viet Cong deserter camp, the Thu-Xa "Open Arms" Center, where they spoke with a former Viet Cong lieutenant who explained why he joined the communists and why he decided to desert.

During part of their tour they were accompanied by U.S. Ambassador Henry Cabot Lodge and General Paul D. Harkins, commanding general, U.S. Military Assistance Command, Republic of Vietnam.

McNamara and Taylor were briefed at combined American-Vietnamese conferences at which Harkins and top Vietnamese commander were present. Harkins and other U.S. military leaders here have discounted pessimistic reports on the progress of the war and are known to favor full support for government forces.

In the IV Corps area, which covers one-fifth of the Republic of Vietnam's total territory, McNamara and his party saw a display of captured communist weapons. These included a communist Chinese recoilless rifle, an American .50-caliber machine gun, British automatic rifles, Czech machine guns and Russian rifles.

Appearing to be impressed, McNamara commented, "That's a fantastic amount of force."

The IV Corps area is infested by nearly half of the estimated 25,000 Viet Cong communists operating in this country.

McNamara spent several hours conferring with President Ngo Dinh Diem before winding up his visit.