* Israel says it will deport pro-Palestinian activists
* Hundreds of police deployed at Tel Aviv airport
By Jeffrey Heller
JERUSALEM, April 15 (Reuters) - A pro-Palestinian "fly-in" to Tel Aviv got off to a slow start on Sunday after Israel scrambled to block activists from boarding flights in Europe.
"Four activists have been detained after arriving on an El Al flight from Paris and are being questioned at (Tel Aviv) airport," police spokesman Micky Rosenfeld said.
An Interior Ministry spokeswoman said the Immigration Authority had on Wednesday given airlines the names of some 1,200 activists whose entrance to Israel would be barred. Israel made clear the airlines would have to shoulder the costs of sending any deported activists back to their port of origin.
Leehee Rothschild, a "Welcome to Palestine" activist, said that dozens of campaigners had since been informed by airlines that their tickets to Tel Aviv have been cancelled.
Organisers said some 1,200 Palestinian supporters throughout Europe had bought plane tickets to Israel and had planned to travel on to the occupied West Bank, an hour's drive from Tel Aviv, as part of a campaign called "Welcome to Palestine".
The aim of the so-called "flytilla", organisers said, was to help open an international school and a museum in Bethlehem. But Israel has denounced the activists as provocateurs and said it would deny entry to anyone who threatened public order.
Hundreds of police officers were deployed in and around Tel Aviv's Ben Gurion Airport, Israel's main gateway to the world.
"We are expecting hundreds of activists throughout Sunday. Some will be sent back to their countries. As part of normal procedure, they will be questioned and each case will be decided upon individually," Rosenfeld said.
A similar, though smaller "fly-in" last year led to a few hundred activists being blocked at European airports and more than 100 others were deported after Israel denied them entry.
"Israel's willingness to detain people who have not committed any crime and have done nothing but say they came to visit Palestine is a hysterical reaction," Rothschild said.
Palestinians hope to establish a state in the West Bank and East Jerusalem, areas Israel captured in the 1967 Middle East War, and the Gaza Strip that is ruled by Islamist Hamas.
The office of Israeli Prime Minister Benjamin Netanyahu released a letter on Saturday which it hoped to hand the activists upon their arrival.
Echoing the "thank you for choosing our airline" announcements cabin crew often make to passengers after landing, the letter said: "We appreciate your choosing to make Israel the object of your humanitarian concerns."
"You could have chosen to protest the Syrian regime's daily savagery against its own people, which has claimed thousands of lives," the letter read. "You could have chosen to protest the Iranian regime's brutal crackdown on dissent and support of terrorism throughout the world."
"But instead you chose to protest against Israel, the Middle East's sole democracy ... We therefore suggest that you first solve the real problems of the region, and then come back and share with us your experience. Have a nice flight."
Israel's left-wing Haaretz newspaper criticised the government's decision to bar the activists.
"A country that respects human rights in the territories under its control, including the right to non-violent protest against foreign occupation, must invite peace activists to visit anywhere and welcome them with flowers," it said in an editorial. (Editing by Jon Hemming)