Sen. Edward M. Kennedy (D-Mass.) kicked off the week-long 73rd annual convention of the National Association for the Advancement of Colored People here this morning with a sharp attack on the Reagan administration. Cheers and applause interrupted his speech dozens of times.

Calling Reagan's the "most anti-civil rights administration in the history of this land," Kennedy zeroed in on the president's current economic policies.

"Today 50 percent of black youth are out of work," he said. "In many inner cities, far more than half of an entire generation has been left without any opportunity at all. No American in this rich land should be denied help or hope or left at the bottom of a mountain of unemployment," he said. "The Reagan cheese lines of 1982 are as unacceptable as the Hoover bread lines of 1932."

Urging that the third year of the Reagan tax cut should be repealed, Kennedy said, "The administration claims to have a social safety net. But, in fact, the only social safety net now in place is the one that protects the special privileges of the very wealthy. I reject their cruel and unfair theory of government of the rich, by the rich, and for the rich."

Kennedy has long been a favorite at NAACP conventions, and as he concluded his speech, an organ in the hall began to sound the strains of the old civil rights protest song, "We Shall Overcome." Several thousand delegates--including Kennedy, his son Patrick and others on the stage--joined hands and began to sing, swaying back and forth.

Well over 10,000 persons are expected to attend the week-long convention, including the delegates, their families and interested observers and supporters.

This year's convention has two major themes. One is the Reagan economic program, whose cuts in welfare, education, job training and nutrition have had a disproportionate impact on the black community. The other is black voting, and with the strengthened extension of the Voting Rights Act approved by Congress this month, the NAACP is holding a drive to persuade blacks to register and vote to repudiate Reagan's policies in the November elections.

Boston, which was chosen five years ago for this convention, has had major racial problems, especially since the start of court-ordered school busing in 1974, and security has been a subject on the minds of many delegates.

Deputy Superintent Paul Johnson of the Boston Police Department said today he has been given "authorization to use whatever resources the department has" to prevent any kind of racial incident or confrontation during the convention.

Although a Ku Klux Klan chapter apparently applied for a permit to demonstrate, Johnson said no permit was issued. He added that police patrols have been increased in the city's racial trouble spots, as well as in the vicinity of historical monuments the conventioneers might want to visit.

Former Vice President Walter F. Mondale is scheduled to address the group later this week. No high-level member of the Reagan administration was invited to speak. Reagan addressed the convention last year and received a polite but chilly reception.

Kennedy, whose reception was anything but chilly, came to Boston directly from the Democratic party's mid-term conference in Philadelphia, and there were repeated references to his 1980 presidential campaign and his possible 1984 candidacy.

He criticized a number of administration changes in civil rights enforcement, but singled out the administration's decision to change policy to allow tax-exempt status to schools like Bob Jones University that discriminate on the basis of race.

"Bigotry is not the message of Jesus Christ. . . . In reality, Bob Jones University is nothing more than Jim Crow University . . . ," he said, "and tax exemptions must not be granted for racial prejudice in segregated schools or colleges."