Even when Diron Adams was toppling building blocks in day care, his mother knew he wasn't like other children. He wasn't just a quiet child. He struggled to form sentences. When other children were reciting their ABCs, the concept of an alphabet seemed beyond Diron's grasp.

Last year, Diron entered first grade at Belle View Elementary in Fairfax County. But reading and arithmetic proved to be insurmountable hurdles, and Diron, who is now 8, was held back.

For two years, Diron has been in a Title I class, a program designed to help children with learning problems. With the help of that class, he is pulling even with the rest of the children his age. He has begun to read and to enjoy the schools days that were once so frustrating to him.

But Diron's mother Nancy has been told his progress could be derailed shortly. Under proposed cutbacks in federal aid to education and other social service programs, Nancy Adams has been told, there might not be money to help children like Diron.

The Reagan administration wants to cut 25 percent from the Title I funds this September. Last week, speaking for her son and the 2,700 other children in Fairfax County's Title I programs, Nancy Adams took her case to Capitol Hill.

"This program deserves to have more money, not less," she testified before the House Education and Labor Committee. "I've been in the classroom and seen my child grow. Title I works."

Adams, 32, shared the witness table with Phyllis Ellis, who has two children, Stephanie and Shawn, both described by Ellis as slow learners. Eight-year-old Stephanie is enrolled in a Title I program that's helping her through second grade at Louise Archer School in Vienna, but Ellis, 33, came to talk about Shawn.

"I'm mainly here because of my son," she said. "I didn't know about Title I when Shawn first had trouble at school, and he missed the special classes. Now he's 15 and attending the eighth grade in a learning disability, self-contained classroom.

"In three years, he'll have to register for the draft. He still has trouble reading."

Title I isn't the kind of social service program that makes headlines -- no children going to bed hungry because food stamps have been stopped; no elderly Americans freezing to death because the budget cutbacks eliminated their fuel assistance payments.

But parents and educators say the effects of Title I cutbacks could be just as dramatic, if less visible.

To Adams and Ellis, it means their children might not achieve their full potential, or even a fraction of it.

Begun in 1965, Title I is the nation's largest federal aid program for elementary and secondary education. This year, nearly 6 million students in 90 percent of the nation's school districts will participate in Title I. The program is designed to meet the needs of any student with learning problems, and although it benefits primarily low-income children, educators say children from all income levels are served by Title I.

The average cost of the program is $450 per pupil, according to the Children's Defense Fund, an advocacy group that predicts more than 1 million children would be dropped from the program if Congress approves the Reagan administration plans.

For Fairfax County that would mean a cut of $450,000 out of its current Title I allocation of $1.8 million."Fewer children would be helped. That's the bottom line," said Gloria McDonnell, director of the Fairfax County program.

McDonnell said 90 percent of the budget is devoted to teachers (70 with six aides). "There's very little waste," she said.

This year, 750 youngsters are taking part in Arlington County's Title I program, under a federal allotment of $400,686. Alexandria has 1,050 children in Title I with $595,935 in federal funding. Under the administration proposals, funds for both programs face reductions.

In addition to the 25 percent cut in funds, Republican economic planners are expected, as they have with other social service programs, to propose that control of any remaining funds to switched from Washington to the states. Under than plan, localities would be given "block grants" to disburse at their discretion. Currently, Title I funds are earmarked specifically for the program and can be used for no other purpose.

"The schools are there and they can contribute to that program too," said a Republican aide to the House education committee. "The cuts don't have to be in Title I, and local schools can decide where they need money the most."

In the past, however, when the federal government lifted rules limiting how funds could be used, local districts have rarely given full funding to special programs such as Title I, according to the Children's Defense Fund.

"It's very clear to me that Title I has made a substantial contribution to schools throughout the country as well as here," said Fairfax Superintendent Linton Deck in an interview last week. "It has assisted principals and teachers in ways I don't know how you could gauge, but it's very significant."

Deck noted, however, that Fairfax schools already have begun studying ways to come up with contingency funds in case the Reagan cutbacks are approved.

Title I enjoys broad support among Democrats and many Republicans on Capitol Hill, especially in the House education committee, although Democrats have been among the more vocal supporters in recent weeks.

"Title I is working," said Rep. George Miller (D-Calif.) at the hearing where Adams and Ellis testified last week. "We want to save it."

Backing words with action, the panel has recommended that the House not only override the administration's proposed cutbacks but add more funds to the social service budget, including Title I. The committee vote was along strict party lines, with the 20 Democrats on the committee voting to support the recommendation, and the 14 Republicans voting against it.

"My priority is 100 percent all the way for all these programs affecting children," said committee Chairman Carl Perkins (D-Ky.) in an interview after the hearing.

But that priority could very well be overruled by the White House and Republican-dominated Senate.

At least for the remainder of this school year Title I is safe, and until classes end in June, Diron Adams will continue to get the help his mother considers so important to his educational progress.

Every day, Diron has a 10:15 a.m. appointment on the second floor of Belle View school. There, a specially trained teacher works with Diron and five other children in a program called SULA, short for Step Up in Language Arts.

Last Monday, the children played a game called "What's This?" The teacher hid a mysterious object in a box and gave the children clues: It was "red, round and you can eat it." An apple, they guessed, and then took turns giving the teacher some clues at discovering what they put in the box.

"The idea is to make them think," Nancy Adams explained. "Diron beams over little things like that, which to them are such big stepping stones on the way to reading."

Last year, Diron wrote a book during Title I classes. He composed the rought draft, edited the copy and illustrated the final product. The book was bound and unveiled at a young authors' show at the end of the year.

"He takes great pride in that," said Adams. "Diron's father was a poor reader and didn't graduate from high school and he doesn't want to see that happen to his son.