The Siamese twins separated 16 days ago at Johns Hopkins Hospital are making slow but steady progress toward regaining normal mental abilities after two weeks of drug-induced sleep, doctors reported yesterday.

The 7-months-old boys, who had been joined at the head from birth, spontaneously open their eyes and move their arms and legs as they lie in separate cribs, doctors said.

But Patrick and Benjamin Binder do not yet smile at their mother, reach for objects or show the kind of alert responses normal for infants of their age, said Dr. Mark Rogers, director of pediatric intensive care at the hospital.

The infants have reacted to the touch of dolls their parents have brought them but do not spontaneously reach for them or hold them, he said.

The twins are like other small children who incur traumatic head injuries, enter a coma and emerge through a semicomatose state for some weeks before reaching their final level of alertness, Rogers said in an interview yesterday.

The twins remain in critical condition, and their survival is not assured. But no serious infection has developed in the extensive wounds created by the surgery. The twins are breathing satisfactorily using a respirator and are receiving normal infant formula through a nasal tube.

One key question is whether they will show brain damage from the 22-hour surgery, during which oxygen to their bodies was reduced. In similar cases, separated twins have suffered brain damage and paralysis.

Rogers said the infants have reacted to pain by kicking and squirming when needles are used in changing intravenous tubes. They also react to light being shined in their eyes, sometimes open their eyes when touched and have made guttural, gurgling noises.

While they react to touch and may move or open their eyes when their parents touch them, the action is a reflex, apparently not a sign that the boys recognize their parents, doctors said.

The parents, Josef and Theresia Binder of Ulm, West Germany, visit daily for a few hours, especially in the mornings, Rogers said. The children remain in a sleeplike state most of the time even though barbiturate drugs used to sedate them for two weeks have been completely withdrawn for several days.

Rogers said the children are doing about as well as doctors might have predicted before the operation. "But, of course, we had hoped they'd be doing a lot better," he said. "But it was just a hope."

Rogers told reporters yesterday that "there are certain periods we have passed . . . . Right now, we are more hopeful they will survive. If we keep them going long enough, we still have a potential for them to have a real, honest-to-goodness recovery."

He said he could not predict their chance of survival or complete recovery. He said two to four weeks should pass before the twins are expected to make major progress in showing alertness.