Assad Kamel Abu Jazzar, who lives in one of the most crowded stretches of real estate in the world, got a breath of fresh air today. It was a long time coming.

He awoke before dawn, stuffed 300 Israeli shekels--about $70-- in his jeans' pocket, packed a change of clothing and a bag lunch and--for the first time in six years--set foot outside the teeming, destitute Palestinian-ruled part of the Gaza Strip.

"We've been like in a siege," said the 20-year-old Palestinian, smiling broadly in the midday sun and savoring his newfound sense of liberty. "Between the sea on one side and the border on the other, we haven't been able to go anywhere. It's like being in prison."

The gates of Gaza swung open today for Abu Jazzar and about 425 other Palestinians, nearly all young men in their twenties. After four years of delays and weeks of 11th-hour haggling--even after peace talks were revived last month--Israel inaugurated a safe passage connecting the two areas of Palestinian-run land, in the Gaza Strip and the West Bank, that are separated by Israeli territory.

Palestinian leader Yasser Arafat and the late Israeli prime minister Yitzhak Rabin agreed in an interim peace deal in 1995 to open a route that would allow Palestinians to make the passage without Israeli interference. Since then, it has been postponed repeatedly by Israeli governments worried that it would pose a security risk.

Right-wing Israelis opposed it, arguing that Palestinians determined to attack Jews could easily turn off the designated route and slip into Israeli communities to do so.

"We have every reason to be scared and to be careful," said Haim Gross, 24, a religious Jew who said his brother was killed by a Palestinian in 1983. He was among a small group of protesters posted near Gaza's Erez Crossing today as the Palestinians' buses and taxis rolled by on the way to the West Bank.

Despite such fears, Israelis promised not to use the right of way to trap and arrest Palestinians wanted for past terrorist attacks--although they will deny crossing permits to any such suspects.

The difficulties in crossing between the two areas began shortly after the 1993 Oslo agreement between Israel and the Palestinians, which revolutionized Middle East peacemaking. Since then, after the number of terrorist incidents against Israelis rose, Israel has required passes and permits for Palestinians seeking to enter the country for work, business or personal reasons.

More than 35,000 Gazans have permits to work in Israel, and many more people from the West Bank cross into Israel legally or illegally every day. But until now, the passes that allow entry into Israel for work have generally not permitted a Gazan to cross into the West Bank, or a West Bank resident to go to Gaza. Today that changed.

Those who have no record of security arrests will receive a magnetic swipe card that allows them to ride in taxis or buses across Israeli territory; it will be valid for one year. Those who have a security record in Israel will be able to travel on Mondays or Wednesdays in a convoy of buses escorted by Israeli soldiers.

For thousands of Palestinians, to whom the Middle East peace process has paid paltry dividends since it began in 1993, the route holds the promise of real improvement in their wages, prospects and horizons. For Arafat's Palestinian Authority, the corridor is viewed as a lifeline uniting two geographically discrete regions that could soon make up an independent Palestinian state.

The 34-mile corridor, which uses existing roads to cross Israel, will be open during daylight hours for traffic between two territories that have grown increasingly estranged in recent years. It will operate year-round except for three major Israeli holidays.

In theory, the traffic is to be two-way between Gaza's Erez Crossing and the Tarqumiya junction near Hebron, just beyond the Israeli border with the southern West Bank. But today, only 17 from the West Bank crossed west to Gaza. It was Gazans--poor, cramped, underemployed and deeply frustrated--who flooded out of the strip in fleets of taxis and buses headed east to the bigger, richer, more cosmopolitan West Bank.

"I'm excited, and I'm looking for a change," said Maji Rafati, 20, a day laborer who was 6 years old the last time he left Gaza. "In the West Bank, the streets are cleaner, the people are nicer, and standards of living are much better than in Gaza."

For many Gazans, it was their first real taste of life outside their steamy strip of land by the Mediterranean. A few dozen, traveling in a bus, broke into song on their way and had to be hushed by the driver, who was nervous that he might be stopped by Israeli police before reaching the West Bank.

Others gazed out the bus windows at Israel's landscape, with its orchards, greenhouses and tall cypress trees, lush and sparsely settled by comparison to Gaza's sandy soil and streets strewn with garbage. Before today, some had seen Israel only across the Gaza border's barbed wire fencing, and they marveled.

"If we had all these trees in Gaza, we would have chopped them down immediately," said Hatem Abu Muhsin, 22, a student who pronounced himself thrilled to be traveling anywhere outside Gaza for the first time.

Some analysts worried that the Gazans, poor cousins to Palestinians of the West Bank, would receive a cool reception if they continue to arrive by the hundreds every day, competing for coveted jobs, driving down wages and stirring social tensions in West Bank cities.

"It will advance the idea of having these two areas as one state," said Ghassan Khatib, director of the Jerusalem Media and Communication Center, a Palestinian research organization. "But there might be some negative side effects."

To date, about 2,500 Palestinians, most of them Gazans, have been issued safe passage permits. Israel denied permits to 84 Palestinians for security reasons, including some Gazan journalists who apparently were blacklisted because of their contacts with militant Islamic groups, such as Hamas, the Islamic Resistance Movement.

Israel says it expects about 1,000 Palestinians will make the crossing, which takes 45 minutes to an hour, each day. Security will be tight; every Palestinian must put his luggage through an X-ray machine and pass through a metal detector. Their taxis and buses will be carefully monitored by Israeli computers to ensure that every Palestinian who begins the trip arrives at the other end in the allotted time.

Another, more northerly route for Palestinians is expected to be opened next year.

CAPTION: At an Israeli checkpoint, Palestinians wait in line for processing before being allowed to travel along the newly opened safe passage between the Gaza Strip and West Bank.