As the crack problem grows ever larger, its victims have become ever younger. The latest two - an 11-year-old alleged to be a drug courier and a 10-year-old crack dealer - left officials wondering if they're losing the drug fight.

"Crack and drugs are so pervasive that of course it trickles down into the lower grades," said Paul Berczeller, a spokesman for the United Federation of Teachers. "You have young kids used every day as drug runners."Ginay Marks, a Brooklyn school board activist for 17 years, agreed: "I would say in terms of crack - and we thought heroin was an epidemic - nothing has spread with such rapidity among our school children."

The two grade-schoolers arrested in separate incidents less than three weeks apart offered examples of both street and school incidents, authorities said.

The 10-year-old was arrested Jan. 15 after police watched him and a 14-year-old partner make a half-dozen crack sales in Wyandanch, Long Island. The 5-foot-tall boy had three $20 vials of crack and $226 cash on him when arrested.

A Family Court judge ruled Wednesday that he had committed the crimes and scheduled sentencing for Feb. 10. The boy faces up to 18 months' detention in a youth facility or two years' probation. Charges against the 14-year-old were pending.

On Tuesday, an 11-year-old boy arrived at his Bronx elementary school carrying what looked like his lunch bag. Inside, school officials found 411 vials of crack, most in 10-packs worth $50 apiece.

The special education student told police his 17-year-old brother had given him the drugs. A search was on Wednesday for the brother, said police spokesman Officer Hugh Barry.

"When an 11-year-old child with special learning needs is exploited as a drug carrier, it reaffirms my belief that drugs are the most serious problem our youth must confront," said Schools Chancellor Richard Green.

Local School Board President Lawrence A. Warden, whose Bronx district includes the school that the 11-year-old attended, said he was "shocked and angry" after the arrest.

"We don't expect that from an 11-year-old youngster. It's like carrying a loaded machine gun in a playground," said Warden.

Board of Education spokesman Robert Terte, saying much of the problem is on the streets around the schools, noted that the number of drug arrests on school property was down in the past year. In 1987, the figure was 114; for 1988, it was 94.

"Remember, you're talking about 180 school days, with nearly 1,000 schools and 940,000 kids," said Terte. "In percentage terms, that's a very small number."

But Berczeller said the increasing drug problem was at least partially responsible for the increase in violence against teachers in the city. For the period Sept. 1-Dec. 1, 1988, 188 teachers were assaulted; for the same period in 1987, the figure was 119 teachers - a 58 percent jump, he said.