Children's Hospital, which spent almost $80 million to build and move from cramped but underused facilities to a dramatically modern hospital last year, is finding that its new facility is attracting more patients.

Fugures kept by the hospital for its monthly occupancy rates show a substantial and steady increase in the number of patients from birth through 18 years.

One of the reasons for moving the hospital from 13th and W Streets NW to its new location on Michigan Avenue NW was a belief that the old facility - which had occupancy rates of about 60 per cent annually - was underused because inadequate parking and poor security discouraged parents treatment.

The new hospital has 1,000 parking spaces - 2 1/2 times the number at the old facility - located underneath the hospital, providing better security than was available at the old location.

In addition, the new building provides the most modern equipment and facilities available for treating and caring for children - including a bed for a parent in every patient room.

After a slight increase in July 1977 over the same month for 1976, Children's had a steady increase in its occupancy rates so that hospital officials now estimate that Children's is operating at about 70 percent of capacity. In January the hospital increased the number of beds from 220 - the same number it had in the old facility - to 236. The hospital has the ability to operate with a total of 268 beds.

At the same time that Children's moved to its new building it raised the daily room charge from $160 to the current $185 - an increase of about 15 percent.

Children's administrator Noel Kroncke said he would be satisfied with any occupancy rate higher than 75 percent, but he discounted the probability that Children's could achieve a rate higher than 80 percent - the level often cited by health officials as the minimum for efficient operation. Kroncke said that for a pediatric hospital to run at higher than 80 percent would require a number of days of more than 100 percent occupancy, "and I think that's unrealistic."

Kroncke said he did not know where the additional patients were coming from. He attributed the increases to the desire of parents to have their children in modern facilities, the greater ease with which surgeons could obtain time in the hospital's 11 operating rooms, the facilities for parents to stay with their children, better security and parking.

According to Kroncke, the higher occupancy rates at Children's are in line with the experience of two other children's hospitals - one in Detroit and the other in Philadelphia - that opened in the last five years. Both increased their occupancy rates after moving and maintained the higher rates, he said.