After a month of protests and angry rallies by groups that consider the movie blasphemous, Martin Scorsese's ''Last Temptation of Christ'' opened today to long lines, sold-out theaters and scattered picketing.

People eager to buy tickets greatly outnumbered the protesters in all of the nine cities where the movie opened this afternoon. The largest number of demonstrators turned out in New York, where by early evening more than 500 people, many of them Greek Orthodox, were packed into a cordoned-off area in front of the Ziegfeld theater, with 100 police officers looking on. But the number of pickets remained small in other cities.

Several prominent movie directors held a news conference in Los Angeles this morning to defend Mr. Scorsese and the companies that financed the movie, Universal Pictures and Cineplex Odeon Films. 'Only a Movie'

In many cities the people waiting in line were defiant about their right to see the film. When one picket at the Century City Cineplex in Los Angeles admonished ticket buyers, many of the 150 people who were in line at 10:45 A.M. yelled back that they had the right to see the movie if they wanted to. In response to placards with the word ''Blasphemy,'' a man in the ticket line waved a sign that said: ''It's only a movie.''