This year will bring 91 new schools, 50 new school-safety officers, and the end of classroom coffee klatches, Mayor Bloomberg announced yesterday, as the city’s 1.1 million students started the new public school year.

After greeting students at Brooklyn’s Thomas Jefferson High School with handshakes and a few autographs, Mr. Bloomberg stood before a line of television cameras set up in the school’s library and said he means business.

“You are not going to be able to come to school and use it as your clubhouse,” Mr. Bloomberg warned.

“You are not going to be able to sit in the halls and think that you can just sit there and have a good time with your friends,” he said. “We used to have children who would walk into class, go in the back of the room, tell the teacher off, pull their chairs around, and have a coffee klatch, and then walk out. We’re not going to tolerate that anymore.”

Police Commissioner Raymond Kelly, who joined the mayor, said he’s taking the lessons learned last year at the 12 “impact schools” citywide.

“We have expanded the list of schools that will get extra attention by 30,” he said. “We’re optimistic about the affect we’re going to have on the additional 30 schools.”

Schools Chancellor Joel Klein and Mr. Bloomberg said schools with violence problems wouldn’t be called “impact schools” anymore.

The Police Department, working in conjunction with the Department of Education, would simply send resources to places where problems arise.

Fifty new Police Department-trained safety officers paid for with Department of Justice money will help keep the schools safe. The new officers will bring the police force in the schools up to 200 officers.

By most accounts, yesterday was a fairly smooth first day.

The teachers’ union president, Randi Weingarten, said the later-than-usual start to the school year made open ing easier because officials had time to work out “staffing glitches” before students arrive at school.

She said the biggest problem is no surprise – the budget problems that teachers and principals have been talking about since June.

“Lots and lots of high schools are suffering from significant budget cuts,” she said, adding that the cuts were leading to higher class sizes and the eliminations of deans, assistant principals, guidance counselors, and other school staffers.

She said she and the principals’ union president, Jill Levy, would meet this week with the education department to try to clear up the problem.

City Council Member Eva Moskowitz, who heads the committee on education, said school snafus typically emerge in the first week rather than the first day, but she said so far it seems like the biggest problems are related to enrollment.

She said she got calls yesterday from parents whose children were in “utterly unacceptable” schools, and others who had been bounced around all day from principals to enrollment centers to regional offices.

Students who weren’t enrolled at any school or who weren’t happy with where they were going had the roughest day yesterday.

Lines were long at the high school enrollment center at 110 Livingston Street. The line was extra long because students who were dissatisfied – rather than just unenrolled – showed up even though the center was created for people with no place.

The public advocate, Betsy Gotbaum, referring to her visits to other enrollment centers in Jamaica and Flushing, said “the long lines of high school students awaiting placement moved quickly.”

But she said one center that was supposed to close at 1 p.m. shut down at 11:50 a.m.

“If what my office saw is any indication of what happened at centers across the city, then hundreds and maybe even thousands of students got turned away today without a school to attend tomorrow,” she said.

Mr. Klein spent the day on a five-borough tour of city schools. After Thomas Jefferson, he read part of the book “Miss Nelson is Missing” in a third-grade classroom at P.S. 22 in Staten Island and participated in a fifth-grade circle dance class at P.S. 50 in Manhattan.

Then he traveled on to a new charter school, the Bronx Lighthouse Charter School, in the Bronx, where he greeted children and talked about how three schools can learn from each other while sharing one building.

The highlight of his tour came at his last school visit, at Flushing International High School in Queens, where he jumped into a basketball game in the gym and sunk a three-point shot.