The first significant wave of mailed legalization applications began showing up in the Department of Immigration and Naturalization Service processing offices this week, officials reported. Jane Arellano, INS deputy district director for immigration reform, estimated that about 800 mailed applications had arrived at the agency's local legalization offices since the weekend. Last week, the offices began granting interviews on a walk-in basis to immigrants because so few applications had been mailed in at that point. Once the mailed application forms begin arriving in a steady stream, Arellano said, the offices will begin setting up appointments for legalization interviews. INS officials also said that as of Tuesday, more than 350,000 application forms have been given out in the Los Angeles area since April 27.