CLARK AB, R.P. — Twenty American returnees from North Vietnamese captivity landed at this base Sunday night and were given a larger and more rousing welcome than another group, seven times as large, that landed six days before.

At least 3,000 servicemen and their families crowded the sandy end of the flight line and struggled for positions along the end of the long tarmac-making the crowd a third larger than the one that turned out last Monday to greet 142 returnees. All those men have since been flown to hospitals near their homes in the U.S.

To Americans here, there was no such word or attitude as anticlimax. Tiny American flags fluttered along the human fence like multi-colored flowers. So many cars were parked on the dry, brown lawns near the flight line that the area resembled the approaches to a ball park.

Deafening cheers rose as a C141 StarLifter, its red lights winking, touched down at the far end of the field at 6:39 p.m. They echoed through the shrill roar of jet engines as the huge plane taxied up and turned broadside to the crowd.

The mechanics of such a welcome were by now basic. A red carpet was rolled out to a yellow passenger ramp, a color guard stood by with the American and Philippine flags, the senior officer among the returnees, Navy Cmdr. James G. Pirie, Tuscaloosa Ala., debarked first, slashed off a snappy salute at the top of the ramp, and descended in a few steps to grasp hands with Vice Adm. Damon W. Cooper, commander of Task Force 77, Lt. Gen. William G. Moore Jr., 13th Air Force commander, and U.S. Ambassador to the Philippines Henry A. Byroade.

Pirie, who was shot down June 22, 1967, stepped to a loudspeaker and said:

"It's been a long time. Seeing the American flag over here just defies description of my emotions. We are proud to be Americans. We are proud of our commander-in-chief, President Nixon. We are proud of the Americans. who have supported us over the years. We all look forward to seeing our families very soon and we want to thank you all for this welcome — it's beyond what we expected, but we certainly appreciate it. Thank you so very much."

Then he walked down the carpet with a dignified stride — once allowing himself a smile and a sporty wave at the crowd. The 19 others filed out and briskly followed Pirie's example — as they had a few hours before at Gia Lam airfield outside Hanoi. Lt. Col. Richard F. Abel, an Air Force officer who flew into Gia Lam with an 18-man advance party, that dickered with the Vietnamese for the release, said the 20 men were brought to Gia Lam on a bus. As they got off, Abel related, Pirie formed them up in two even 10-man ranks and marched them in brisk fashion to the exchange area. Each man who stepped up to him, Abel recalled, said "Reporting for duty, sir!" in a clipped, unfaltering voice.

On the plane, Abel said, Pirie was still very much in charge. He told the men they would leave the gray jackets and small black handbags the North Vietnamese gave them and debark only in their blue prison dress. They would salute once for all three officials, Pirie ordered, and there was no discussion or protest — leading Abel to repeat his earlier beliefs that the men were organized in prison and the reins of rank and discipline were kept taut.

Abel said this flight was like another he had made with the first group of returnees last week — the prisoners filed aboard the StarLifter quietly and then cheered as soon as they were aloft. They exchanged handshakes and backslaps once more as the StarLifter swung over the South China Sea and the coastline of North Vietnam dropped away.

Now they were at Clark AB and the flustering delays in the their release had been forgotten — the StarLifter, slowed by bad weather, the exchange itself held up because members of the International Control Commission returned late from an inspection tour.

Lt. Cmdr. Fred R. Purrington, who comes from North Dartmouth, Mass., and had been held since Oct. 20, 1966, walked more slowly than Pirie, but his step was firm and graceful. After Pirie walked into a blue ambulance bus, the others debarked on his orders in "shootdown order" — by date of capture.

Air Force Capt. John J. Naysmyth, Jr., who was shot down Sept. 4, 1966, was unquestionably qualified to follow the Navy officer.

Maj. Jay R. Jensen was so excited that his hand fumbled past those of the general and the admiral and gripped that of Byroade, who stood at the end of the reception line. Cpt. Joseph C. Plumb, a Kansan held by the North Vietnamese since May 19, 1967, looked grave and proud. Capt. James R. Shibely, Spokane, Wash., beamed as someone shouted "Go get 'em, baby!" Capt. Joseph E. Milligan, Asbury Park, N.J., clasped both hands around those of the two officers and the ambassador. All of the men walked and nobody debarked on litters or crutches.

As the last man boarded and the bus pulled away, several returnees gave the thumbs-up "all systems go" sign. They reached down to grasp the hands of air policemen and then several people who leaned precariously over the orange nylon cord that cordoned the flightline.

A small boy suddenly rushed out to the bus and handed something up to a returnee. Several other children followed and harried air policemen had to scatter "the small intruders" and the newsmen who moved around with flashing cameras.

A returnee waved one of the gifts that had been thrust at him — a large paper rose.

Maj. Joseph S. Abbott Jr., Alloway, N.J., could feel more securely informed about the world that awaited him than other returnees. As he rode back on the plane to Clark, Abbott reached into a grab bag of newspapers and magazines and came out with a copy of Time — one that had a picture of his family on the cover and a story of what had happened to them during his almost five years of imprisonment.

"He read and grasped it as if it was priceless," one of the officers in the advance party told newsmen. "It told him many things he did not know." Abbott has seven children.

Other returnees, before they are sent home, will be told of family happenings through a dossier furnished to the escort officer provided each man.

Abel said he spoke at length with one returnee, Capt. Kevin J. McManus, who was a cadet in Abel's squadron at the Air Force Academy. They talked of old times and lost acquaintances.

On the same plane was Capt. Edward J. Mechenbier, Dayton, Ohio, who was McManus' academy classmate and also piloted the F4C Phantom in which both men were shot down on June 14, 1967. Imprisoned together, they were also liberated the same day. While McManus was supposed to get off the Starlifter first, he as weapons systems operator stepped aside to let his aircraft commander precede him.

Like the returnees who preceded them, the men released Sunday were taken to the base hospital for processing and medical checks. The men appeared to be in good health and are expected to be on their way "in a very few short days," an Operation Homecoming spokesman said.

The returnees ate heartily, the spokesman said. One man put away five steaks and six eggs and said he was going to have another in a hour.

Abel said several of the returnees asked him how South Vietnam was doing.

"I said they appeared to be doing well. Time will tell."