LONDON, AUG. 20 -- Amid mounting calls for a tightening of Britain's gun control laws, Prime Minister Margaret Thatcher interrupted her vacation in southwestern England today to visit the wounded victims of a shooting rampage that left 15 people dead yesterday.

Police in Hungerford, the small town 60 miles west of London where the bloodbath occurred, said that the assailant, Michael Ryan, who killed himself after shooting 14 others, had a license for all the weapons he used. They were a Chinese-made AK47 semiautomatic assault rifle, an M1 carbine and three handguns.

Thatcher, who traveled to Hungerford with her husband, Denis, described the incident as "something unknown to this country."

Asked about changes in Britain's gun control laws, Thatcher said, "If they need to be tightened up, or if we think that it could prevent anything more like this, then of course that will be considered."

Ryan, a 27-year-old bachelor and only child who worked as an occasional day laborer, shot and killed himself last night after police cornered him in a school following a six-hour shooting spree in which he killed 14 persons, including his mother, and wounded 16. Police who had tried to persuade him to leave the school described his attitude then as "lucid and reasonable."

"He expressed concern that he had shot his mother," a widow who was one of yesterday's first victims, Police Chief Colin Smith said. "He expressed the view that it was strange that he could shoot other people but couldn't shoot himself. Shortly after that, a shot was heard."

Hungerford residents today tried to comfort each other, gathering in church services and chatting quietly on street corners. There were stories of heroism, fear and poignancy.

The first person Ryan killed was Susan Godfrey, 33, who had taken her two children, ages 2 and 4, into a nearby woods for a picnic. According to police who have spoken to the children, they had just returned to the car and were strapped into their seat belts by their mother when Ryan dragged Godfrey into the woods and shot her in the back.

The children, police said, managed to get out of the car and started walking down a road. Myra Rose, an elderly woman who lives nearby, was the first person they encountered.

Hannah Godfrey, 4, held the hand of her brother James, Rose recalled, and said, " 'We are coming to find you.' They just put out their hands and held my hands.

"The little girl . . . said, 'a man in black shot my mummy.' "

After leaving Godfrey, police said, Ryan drove into Hungerford, to his mother's home. One of the wounded, Margery Jackson, lives on the same street, and told reporters today from her hospital bed that she saw Ryan drive up as she returned from shopping.

She said she saw his mother run outside the house, where Ryan shot and killed her. Then, Jackson said, he began firing indiscriminately as he walked toward the center of town.

As she ran inside, Jackson said, "I could hear the children screaming outside . . . there were bodies everywhere." Jackson herself was shot in the lower back, through a window, as she helped an elderly neighbor to cover.

No motive has been advanced for Ryan's actions. Neighbors and acquaintances described him as a quiet man, a loner and, according to one former employer, "a bit of a wimp."

But on newspaper front pages across Britain, Ryan was dubbed "Rambo," after the movie character whose combat dress and headband he appeared to have adopted yesterday.

Many Britons believe that such firearms crimes are common in the United States, but the idea that such a thing could happen here has caused widespread shock. As details of the killings, and of Ryan's legal arsenal, have been revealed, many have expressed surprise that such gun collections are allowed here.

The criminal use of firearms in Britain, although rising, still is relatively rare. According to the Home Office, guns were used in a total of 9,363 crimes in England and Wales during 1986, and only 51 were cases of homicide.

But the rarity of criminal gun use masks the relative ease with which most Britons can be licensed to own guns, and can buy them.

Applicants for certificates to own rifles and handguns must present police with a "good reason" for wanting them, a Home Office spokesman said. They must prove that "public safety is not endangered, that they are fit to be trusted with a firearm," and are willing to follow requirements for safe storage of the weapons, he said. Requirements for ownership of a shotgun are less stringent.

A Home Office spokesman said most certificate holders are members of gun clubs.

Michael Ryan belonged to two such clubs. The manager of one said Ryan had last appeared there for target practice less than 24 hours before he began his shooting spree.