As fighting raged in the hills east of Beirut and Israeli planes pounded targets in the western half of the capital, the United States closed its embassy today and evacuated about 450 Americans and Lebanese by boat from this port in Christian-held territory north of the city.

About 310 other persons left on a British vessel. All were to be taken to Larnaca, Cyprus, about 10 hours away.

The evacuations were orderly and calm, with little of the fear and tension that grips predominantly Moslem West Beirut as it waits out the prospect of an Israeli assault.

Typical of the dramatic difference between daily life in West Beirut and in mainly Christian East Beirut, Lebanese fished and water-skied at this port today while other vacationers swam or sunbathed at nearby beach resorts. The eastern sector, dominated by the Christian Phalangist militia, has escaped the damage and deprivation that the Israeli military has unleashed on West Beirut in an effort to crush the Palestinian guerrillas and their Lebanese allies there.

After waiting for several hours under the blazing Mediterranean sun, the Americans being evacuated were taken by launch to two converted 6th Fleet troopships--the Nashville and the Hermitage. According to U.S. Embassy official Thomas Barron, only about 100 of those evacuated were U.S. citizens. The rest were Lebanese and citizens of other countries.

Pentagon sources said an Israeli gunboat approached the Nashville, anchored about three miles off the Lebanese coast, but only "came for a look" and did not harass the American vessel or interrupt the evacuation, United Press International reported.

Those taking the U.S. advice to leave immediately amounted to only a fraction of the estimated 2,500 American citizens living in Lebanon--most of them of Lebanese origin or married to Lebanese.

According to Barron, U.S. officials hope to reopen the embassy soon but have not decided on a new location. The current site on the seafront in West Beirut has been in the line of fire of Israeli gunboats.

Most of the evacuees interviewed today said they wanted to return to Lebanon--when it was safer. They told stories of increasing lawlessness and terror under the armed militiamen of various factions that rule the streets of West Beirut.

For some, the experience was not new. One family had to leave Tehran during the Iranian revolution, and an American said she had been evacuated from Beirut twice before. The departing Americans ranged from middle-aged university professors to a 22-year-old casino croupier from North Carolina.

From Ernest Yaque of Miami, a business trip to Beirut last month turned out to be a case of bad timing. Yaque, a Cuban-born architect for the Hilton hotel chain, had been doing a survey of the Beirut Hilton and Holiday Inn, two of the major hotels gutted during the 1975-76 Lebanese civil war.

Wearing a tasseled red Lebanese fez, Yaque said he had been scheduled to leave June 11 after a month-long stay but got stuck in Beirut when Israeli air strikes forced the airport to close.

"I plan to come back in September if everything is okay," Yaque said. He said he felt obliged to leave now because his family was worried about him.

Another evacuee was Kyle Mitchell, 60, an American pilot for Lebanon's Middle East Airlines and a 27-year resident of Beirut.

He said he was leaving now after so many years of turmoil in Lebanon because this was the first time the U.S. Embassy actually had closed and told its citizens to go. He also said he was fed up with the mounting violence in West Beirut.

"When they get the kids with their guns off the streets, I'll come back," he said. He added that he had left everything in the apartment he has occupied for the past 18 years, which he now risks losing to refugee squatters.

A British pilot, Nicholas Hutton, 49, said he also was impressed by the U.S. Embassy warning.

"When the Americans close their embassy and Israeli Prime Minister Menachem Begin has just come back from the United States, they must know something I don't," he said. Accompanied by his American wife, Katherine, who was evacuated during wars in 1967 and 1976, Hutton said he considered his West Beirut apartment and possessions there a lost cause. He said that in 1975, he lost everything to looters who invaded his home during the fighting between Christian militiamen and an alliance of Palestinians and Lebanese leftists.

For Norman Lofland, a drama teacher at Beirut University College, the prospect of losing his belongings also is not a new one. He said he was forced to leave nearly $5,000 worth of possessions in Tehran when he and his family flew out on one of the last flights before the airport closed during the Iranian revolution.

"We wouldn't leave if we weren't Americans," Lofland said, referring to mounting hostility in West Beirut toward U.S. citizens because of the Israeli invasion. He said he hoped to return to teach in the fall.

Marius Deeb, 40, a Lebanese professor at the American University of Beirut, also said he wants to return for the next term. He said he decided to leave when an Israeli rocket landed 100 yards from his apartment.

"The last 10 days have been terrible," he said. "There has been no electricity except for a few hours and the shelling has been so close to us that at night sometimes we can't sleep at all."

Deeb, who teaches civilization and Middle Eastern politics, said most West Beirut residents wanted the militiamen out but dreaded the prospect of street fighting if the Israelis tried to do it.

"There is a feeling of being trapped," Deeb said.