The first American evacuees from Grenada, 139 medical students at St. George's School of Medicine, arrived here today on Air Force transports with high praise and deep gratitude for their rescuers and reports of continued intense fighting on the eastern Caribbean island.

They told of seeing casualties among the invading U.S. Marine and Army Ranger forces that landed on the island Tuesday morning and reported that sniper fire continued as the second of the C141 evacuation flights left at noon today.

"I have been a dove all my life," said Jeff Geller, of Woodridge, N.Y. "I just can't believe how well those Rangers came down and saved us. Those Rangers deserve a lot of credit. I don't want anyone to say anything bad about the American military."

Their reports, among the first eyewitness versions of events since the invasion early Tuesday by the United States and several Caribbean allies, painted a tableau of fear, bloodshed and chaos among students and citizens of the tiny nation.

"I really loved Grenada, but I fully support President Reagan's move . . . . He really did save our lives," said Grace Brooke, a 1982 William and Mary College graduate who worked last year at Arlington Hospital in Virginia.

The 139 Americans and one British subject who arrived on the first two Air Force flights today said they had set up an emergency medical center on the college campus in the lecture hall and cafeteria and helped U.S. medical corpsmen treat several wounded men from both sides.

"The big psychological problem for me was treating a Cuban who shot two of our men . . . . You see these guys who laid down their lives for you; it was rough," Brooke said.

Matthew Nadler, of Stony Brook, N.Y. said, "There were many wounded; quite a few Grenadans and Cubans wounded. I think most of them had been firing on the Americans, although some were caught in the crossfire . . . . Cuban doctors were brought in by our Rangers to treat their own wounded in a detention center."

The first of the two evacuation flights touched down at Charleston Air Force Base here about 5:30 p.m. and taxied to the main terminal of the Military Airlift Command. The students, some bearded, some bedraggled, some in shorts and T-shirts, some carrying tote bags and tennis rackets, smiled and waved to the applause of a waiting crowd of military people and local residents.

Geller, wearing a white jogging suit with St. George's across the chest, dropped to his knees and kissed the tarmac as he came off the C141 military transport. "The last 10 days have been really hectic," Geller said. "It's just good to be back in the good old U.S.A."

Most of the students were generous in praise of their military rescuers and approved of Reagan's decision to send U.S. forces ashore, agreeing that political instability on the Marxist island was so intense during the past week that they feared for their safety.

Said one student, "God bless America, God bless Reagan, God bless our military."

"I felt we might not make it back," said Mary Guido, a student from Manhasset, N.Y. "I can't say the feelings I have about American citizenship."

Stephen Hall of Hastings, Fla., said, "The military actions and our subsequent return were extremely impressive and we are very proud to have been with the U.S. servicemen . . . .I am very, very proud to be an American."

Other students, however, expressed concern about classmates--mostly upper classmen at the medical school who lived in private homes off the two campuses--who had not been heard from since the military junta that took power earlier this month imposed a "shoot-on-sight" curfew last Wednesday.

After the curfew was imposed, the students were restricted to the school's campuses, with no guarantees of their safety from the Grenadan government and with their food and water supplies dwindling.

Randall Tressler, a first-term student from Jarrettsville, Md., said, "I spoke with a lot of Grenadans on campus and they said they were afraid. The airport was closed, with no sure way for us to get out. They lifted the curfew for four hours and four of us went out for food. We ran the entire distance to a store and were met by a military officer with a submachine gun. It was serious."

Tressler and other students said their sense of isolation grew as phone service was broken off and their water supply dwindled on the campus adjacent to the big new airport being constructed by the Cubans and identified by Reagan as a potential military base for Soviet and Cuban forces.

The students said the Cuban crews in recent weeks had begun round-the-clock construction work on the airport assisted by floodlights and heavy equipment. The airport was quickly seized by U.S. Army Rangers early Tuesday.

Tressler said that he and other students were awakened around 5:30 a.m. that day by gunfire and the sound of aircraft. Pamela Lall, of Boston, said she saw tracer gunfire--she assumed it was warning shots from American forces--hit one corner of the campus. Other students said their dormitories were hit by bullets or shells.

"There was quite fierce fighting," said Steve Renee, of Point Pleasant, N.J. "We imagined the Cubans were resisting . . . . Before this, the Cubans and Russians on the island were not really noticeable . . . . They were in the woodwork, it seemed. Not marching around in formation."

The students also reported that the American invaders encountered some resistance from Cuban antiaircraft batteries ringing the airport construction site.

"I can't explain how dangerous it is," Lall said. "There were snipers all around, even though the military made sure we were secure before we got on the plane today. One Ranger told us they had found 3,000 more Cubans on Grenada than they thought were there."

"This morning," added Grace Brooke, "there were more casualties coming into the school. When I left there were 17 wounded there and some were not going to make it . . . . They were mostly Cuban and Grenadan wounded, held in one area."

Geller said, "The last 10 days have been hectic for us. Last Wednesday we were taking an anatomy test; meanwhile Grenadan prime minister Maurice Bishop and a lot of people were being killed downtown. After that they had a shoot-on-sight curfew. We were really scared and we were confined to our compound.

"We really didn't know what was going on. That was the worst thing."

Steve Berry, of Congress, N.Y., said, "At 5:30 a.m. [Tuesday] I heard machine gun fire. An antiaircraft gun was shooting at this plane that was circling the campus. We went out on our porch and watched them shoot at the plane, and then a helicopter came swooping down and then the paratroopers dropped down."

David Breslin, of East Windsor, N.J., said soldiers came to the medical students' dormitory and "one raised his hands and said, 'Students, we are Americans.' "

"They sent us to the lecture hall. We were there for about 28 hours. We were under the seats for some hours. Then they let us go back to our rooms. We collected sheets, pillows and towels for the wounded. A cafeteria is in the same building. We set up cafeteria tables as beds. They brought Grenadans and Cubans in who were wounded."

"In the library on campus, the Americans were treated. The students helped . . . . It looked like something out of M*A*S*H."

Student Jean Joel, of Albany, N.Y., said that on Monday night "Maj. Christopher Stroud of the new regime talked to us to reassure us of our safety. He said basically it was an internal conflict and above all the nation wanted to stay independent, and we were not involved in the conflict.

"He told us there was going to be an invasion," said Lou Ianniello, of Mechanicville, N.Y. "We didn't believe him. We didn't think he was deliberately lying, we just thought he was ignorant."