Moments after Lillian Janc and her 14-year-old son Jimmy plunged through their living room window to escape from their burning home in Rockville, neighbors rallied to help the family.

The Janc home at 13502 Sloan St. in Rock Creek Manor was leveled last week when a propane gas bottle that the family was storing for a Boy Scout camping trip exploded.

When neighbors heard the explosion, many ran outside to help Mrs. Janc, who had gone back inside to rescue her son, was taken to Holy Cross Hospital with a broken wrist and two burned arms.

A bloodmobile was set up this week in the neighborhood for donations for Jimmy, who suffered second and third degree burns over 50 percent of his body. He was taken to Children's Hospital in serious condition. Arrangements were also made with several area hospitals to accept blood donations for him.

On the night of the fire, Don and Elaine Graydon, who live next door, turned their house into a command center where neighbors could make donations for the family. Since the fire, the Graydons have housed the rest of the family: William F. Janc, a Food and Drug Administration investigator, and his son Tommy, 13, who were away when the explosion occurred, Jeanne, 7, and Kenny, 10. Jeanne and Kenny were only slightly injured.

So far, about $4,000 has been collected for the family, said Graydon. Several area architects have donated their services to help redesign the destroyed home and to find contractors to work at cost to rebuild it. Furniture, food and hardware stores have donated items to the family. The National Geographic Society offered to restore any salvaged photos. Real estate agents are attempting to find the family a rental home in the community and mounds of new and used clothing for the Jances are being stored at neighbors' homes.

Meals have been organized for the next three weeks for the Graydons, while they house the Jances. In addition, nonperishable foods are being collected and stored for the family.

The outpouring from the community has greatly touched the Janc family. Lillian Janc, who is still recuperating at Holy Cross Hospital, was near tears when she spoke of neighbors' contributions.

"We're very grateful to everyone, and with the help of God we'll get through this very nicely," she said.

Mrs. Janc had earlier told her neighbors, Elaine Graydon, "Nothing happens without a reason. I think God wanted people to see just how many loving people there are in the world."

Graydon said that the "giving spirit of her neighbors" has made her realize "that the world's really worth saving."

Janc said his son Jimmy, now undergoing painful skin grafting procedures, has also been cheered by the response.

"He's doing great . . . ," his father said.

Mrs. Janc added, "He's holding up. He's not at all bitter. He's not saying 'Nothing will be right.'"

Little was saved in the fire that consumed the Janc home. Even the family cat was lost. However, a few things did survive: a cedar chest filled with the christening dresses worn by all four children and the dress Jeanne will wear at her first Holy Communion.

Also, two season tickets to the Harlequin Dinner Theater came through the blaze with only its corners scorched. Janc joked, "They must have been made of asbestos, but I doubt if we'll make next month's performance."

Mrs. Janc said, "This has taught me that material things don't mean anything. As long as we have our family, we're happy. I'm not sad about the house, we'll get another, it doesn't bother me at all as long as we'll all be all right."

One thing, however, that her neighbors believe she will miss and which they are trying to replace is Lillian Janc's recipe collection. To that end, they have established a Friendship Recipe File for Mrs. Janc, who according to her neighbors is quite a cook.

Those wishing to contribute a favorite recipe should mail it on a three-by-five card in care of Elaine Graydon, 13500 Sloan St., Rockville, Md. 20853