GAZA CITY, Gaza Strip - A Palestinian detonated a powerful truck bomb at the main pedestrian crossing between Israel and the Gaza Strip yesterday, causing extensive damage that dealt a serious blow to Gazans' hopes of opening up their sealed-off territory.

Although the bomber killed only himself, the magnitude of the explosion - which shook buildings for miles - raised fears that Palestinians are adopting tactics used by al Qaeda, Hezbollah and other extremist groups.

The attack at the Erez crossing also reinforced skepticism about Egyptian-led efforts to bring a truce to the violence-wracked area and hurt international efforts to ease the Israeli-led blockade of Gaza, imposed after Hamas militants seized control of the coastal territory almost a year ago.

Later, at the Karni cargo crossing some 5 miles away, a protest against the blockade turned violent, with Palestinians accusing Israeli troops of firing into the crowd of thousands, killing a 22-year-old man and wounding 16 other people.

The Israeli military said soldiers opened fire after spotting armed men in the crowd, including one carrying an anti-tank missile, and that the gunmen returned fire. *