After a week in which New York City teachers were bludgeoned, slashed, pummeled and blasted, their union leader called Friday for increased security and tougher sentences for teacher assaults.

"One attack against a teacher is outrageous, and to have four in one week is just intolerable," said United Federation of Teachers President Sandra Feldman.Though schools officials insisted the number of attacks on teachers had actually decreased in 3 years, Mayor Edward I. Koch said the city is concerned about teacher safety. He called a "summit meeting" Tuesday of the chancellor, union leaders, the five district attorneys and police commissioner.

The latest act of violence occurred Thursday afternoon when a physical education teacher came upon an intruder rifling through students' gym bags outside a Bronx school and was beaten unconscious with a baseball bat.

Gary Smith, 37, who remained unconscious Friday, was the fourth teacher assaulted. Douglas De Marco was knifed more than a dozen times by a mugger in the bathroom of a South Bronx grammar school.

The other incidents included a teacher who was beaten up by a student and the student's brother and sister, and a 71-year-old teacher who was injured when an M-80 firecracker was tossed into her classroom.

"There's something seriously wrong here," said De Marco, who added that the attack on Smith made him even more "angry and frustrated."

The need for increased security has long been evident to De Marco, who said he teaches in "a neighborhood that's known for two things: heroin and crack."

Yet the Board of Education said the number of assaults in city schools has decreased, mainly because of an increase in security guards in elementary schools.

There were 1,322 assaults in the city's 1,000 schools in 1985-86 and 969 this year, said board spokesman Bob Terte.

But the UFT insists there were about 1,000 physical attacks against teachers both last year and this year. Edward Muir, chairman of the UFT School Safety Committee, said about 20 percent required emergency-room treatment.

Though Feldman acknowledged a decrease in teacher assaults and a rise in security personnel, she said, "It's obviously not good enough."