Israeli Foreign Minister Yitzhak Shamir, eulogizing an Israeli diplomat shot to death in Paris, warned today that Israel will strike at terrorist organizations "without mercy" wherever they seek refuge.

While his threat was not explicitly directed at the Palestine Liberation Organization in Lebanon, Shamir said terrorist groups, such as the one behind the slaying Saturday of Yacov Barsimantov, receive their orders from Beirut. He said the bullet that killed Barsimantov, a second secretary in the Paris embassy, had been "aimed at the heart of the Jewish state."

Shamir's comments underscored a warning made last month by Prime Minister Menachem Begin that Israel would regard the murder of "one Jew anywhere" by a Beirut-based terrorist organization as a violation of the July 24 Israeli-PLO cease-fire and, by implication, as justification for Israeli military action in Lebanon.

The warning came amid rising concern here and in Washington that a serious provocation by the PLO could prompt an Israeli invasion of southern Lebanon similar to one in 1978. Israeli officials, however, have avoided directly blaming the PLO for Barsimantov's death, suggesting that a group trained by the PLO could have been responsible.

In Washington, State Department spokesman Dean Fischer declined to characterize the Paris shooting as a cease-fire violation. When asked by reporters about the U.S. position, he quoted from a past statement that a violation "pertains to all hostile activity from Lebanon into Israel, and vice versa."

The PLO has denied it was responsible for the shooting, which was claimed by a group calling itself the Lebanese Armed Revolutionary Brigades.

Addressing mourners at Barsimantov's funeral in the Holon Cemetery, Shamir said: "I can promise you we will use all the force at our command to crush the terrorist organizations everywhere our hands can find them."

Meanwhile, Assad Halaby, an Israeli policeman who was stabbed by a Palestinian in Jenin on March 24, died today, bringing to eight the number of deaths in the West Bank rioting over the dismissal of three prominent Arab mayors.