Israeli Ambassador to Britain Shlomo Argov was shot and critically wounded late last night while leaving a banquet at an exclusive hotel on a busy central London boulevard. It was the latest in a series of attacks on Israeli and American diplomats in Europe.

An assailant wielding a submachine gun and aided by accomplices shot the envoy in the head, according to police.

Argov was outside the Dorchester Hotel on tree-lined Park Lane across from Hyde Park.

Argov, 52, underwent surgery early today at the National Hospital for Nervous Diseases here, which specializes in neuresurgey. A hospital spokesman said, "He remains critically ill."

His alleged assailant, described by witnesses as Middle Eastern in appearance, was pursued and shot in the neck by Argov's London police bodyguard. A Scotland Yard spokesman, who did not immediately identify the suspect or his nationality, said early this morning, "The assailant is now under guard in the intensive care unit in the hospital but is expected to live."

Two other men were arrested miles away in south London in a car seen leaving the scene of the shooting, police said, adding that a weapon also was found in the car.

Argov had been leaving a black-tie dinner for diplomats and business executives hosted in the Dorchester's ballroom by the De La Rue Co., a British-based currency-printing and security-system firm. Park Lane, along which several major luxury hotels are located, was filled with traffic and pedestrians as limousines lined up outside the Dorchester's ballroom entrance.

Assistant Commissioner Gilder Kelland of Scotland Yard, who was among the dinner guests, told reporters that Argov had walked nearly to his car about 25 yards from the ballroom entrance when his assailant, waiting on the sidewalk, pulled the submachine gun out of a shoulder bag and shot him in the head.

The assailant was described by the waiting Tongan Embassy chauffeur, Moses Hayes, as a short young man who had been standing near the Israeli ambassador's car in front of the show window of an auto dealer-ship next door to the Dorchester. "He was conspicuous because he had a pack on his shoulder," Hayes said. "The ambassador came out and there was a shot. He fell down."

"There was a loud burst of shots just as the ambassador was coming out of the hotel," said British publisher Robert Maxwell, who left the ballroom at the same time.

An armed London policeman guarding Argov chased the assailant down a nearby side street, where he shot him, Kelland said. Witnesses said Argov lay in a pool of blood at the curb alongside his car on Park Lane while the policeman stood over his wounded assailant on the side street until ambulances arrived.

Argov has been Israel=s ambassador here since September 1979. He previously was ambassador to the Netherlands and o Mexico and minister at the Israeli Embassy in Washington. He also had served in Nigeria and Ghana as well as New York and earlier in London, in addition to a period as assistant director general of the Israeli Ministry of Foreign Affairs in charge of the Israeli Information Service.

"We were deeply grieved" by news of the shooting, said a State Department spokeswoman. "We condemn in strongest terms this terrible deed and deeply hope the ambassador will recover from his injuries."

The attack here came two months after a senior attache at the Israeli Embassy in Paris, Yacov Barsimantov, 43, was shot and killed outside his home in Paris. A group based in Beirut, calling itself the Lebanese Armed Revolutionary Brigades, said it killed Barsimantov.

Speaking at Barsimantov's funeral, Israeli Foreign Minister Yitzhak Shamir warned that Israel would strike at terrorist organizations "everywhere our hands can find them." Less than three weeks later, Israeli jets strafed and bombed what Tel Aviv called terrorist targets in Lebanon, citing numerous violations by the Palestine Liberation Organization of the July, 1981 cease-fire there.

The Lebanese Armed Revolutionary Brigades also claimed responsiblity for a submachine gun attack on the annex of the Israeli Embassy in Paris in March, the killing of a U.S. Embassy military attache in Paris, Charles Ray, in January, and an unsuccessful shooting attack on acting U.S. Ambassador Christian Chapman last November.

The Israeli ambassador to Portugal, Ephraim Eldar, was wounded and his Portuguese body guard was killed in a machine gun and grenade attack in Lisbon in November 1979, for which another previously unknown group, the Nasserite Organization for the Release of Detainees in Egypt, claimed responsibility.

No other attacks on Israeli diplomats have occurred here, but London has been the scene in recent years for assassinations of Libyan and Iraqi exiles by fellow countrymen.