Holy Cross Hospital, where more babies are delivered annually than in any other hospital in Montgomery County, has had a birth of its own - a $25-million hospital wing expected to open this week.

And the reason hospital administrators and staff are as excited as new parents is that the project is premature - it has been completed six months ahead of schedule and nearly $3 million below cost.

The project was conceived in 1976 when hospital officials decided to expand the 338-bed hospital, located off Georgia Avenue near the beltway, to 450 beds, said Thomas Burke, a hospital spokesman.

The architectural firm of Faulkner, Fryer and Vanderpool was chosen to design the new facility, aimed at freeing doctors, patients and employes from crowded conditions and adding parking space, The Architects estimated the project would cost $17 million and would be completed by March 1979.

As it worked out, said Burke, the George Hyman Construction Company of Bethesda bid $13.1 million, or nearly $4 million less than the architects' estimate, to complete the project. In addition, the Hyman company, which began work on the project in September 1976, has completed two-thirds of the project ahead of schedule, said Burke.

"The construction company said it will finish renovation of the old portion of the hospital by September - that's six months ahead of schedule," said Frederick Fryer, a spokesman for the architectual firm.

The Hyman company also will renovate the older portion of the hospital, to nearly double the size of the hospital laboratory, at a cost of $1 million. The total cost of the renovation and the addition will be about $25 million when interest is added to the cost of bonds sold for the project.

Hospital officials, archietects and construction company officials said that a combination of well-drawn designs and the coordination between hospital and construction officials are the major factors that have made the project click - both in terms of costs and construction speed.

For one thing, says Roger Cauder, contracts manager for the Hyman company, "We were not hampered by the last two bad winters."

Caudery said the superstructure of the new wing was completed before the winter of 1976, allowing his men to work inside during cold weather. He added that the current winter only caused a minor delay in paving roads around the facility.

And hospital administrator Herbert Bell said costs were cut because "we made an inflexible rule" - no changes were to be made after the architectual drawings were completed.

In the end, however, Bell said there were 10 changes - primarily in redesigning the radiology labs - that cost an additional $100,000.

Costs also were kept down, Bell said, because the project was built during a particularly competitive period in the construction market, which prompted some subcontractors to work for less money.

In the face of the current Washington-area problem of surplus hospital beds, Holy Cross officials are not looking at this project as an unwanted baby. They say the expansion is necessary.

Hospital officials say that for the past four years the occupancy rate for the 338 beds in the older part of the hospital has been 94 percent. They say this situation has forced some patients to stay in the emergency ward for several days because there was nowhere else for them to go.

The cluttered hospital environment, which has forced hospital technicians at Holy Cross literally to work shoulder-to-shoulder and has stolen privacy from patients, has been a continuing dilemma, said Burke.

The problem became so bad at one point that hospital administrators began using parts of corridors and offices for additional surgery rooms and office space.

"Despite the uncomfortable conditions," Burke said, "we have never let patient care suffer because we've been cramped."

The new facility, which includes an expanded emergency room, a larger radiology department, more facilities for single-day surgery patients and a new parking lot that will add 88 parking spaces, will help eliminate the crowded conditions, Burke said.

Burke added that the new wing also will include $2.8 million in new equipment and will result in the hiring of 80 more employes. He said he was not sure how many new doctors would be added to the staff.

The new facility's exterior is an indistinguishable addition to the old hospital, which was built more than a decade ago. Inside the new structure, however, the observer can immediately see that more than a decade of change has taken place.

In the new addition, white walls have blue or red racing stripes depending upon which corridor you walk. The blinking lights of new equipment attest to the updating of the interior. And where patients once had to sometimes be treated in sections of corridors, they will now have private, curtain-enclosed examining rooms as well as new post-surgery recovery rooms.

"This new wing was designed to enhance our patient care," said Burke as he walked along like a proud father, comparing the old facility with the new.

The new facility will mean higher costs for patients, said Burke. "We anticipate that gross charges to patients will increase approximately between 2 and 4 percent as a result of opening the new facility.

"We are still refining data and anticipate submitting a detailed cost estimate to the health service cost review commission in the next several weeks."

Burke said his cost estimates are based on a presumption that occupancy will average approximately 82.5 percent for the year ahead. He said the average medical cost per day for a patient at Holy cross is about $170.

Despite the prospect of increased hospital costs, the project apparently has been well accepted by hospital employes and the public.

Burke said the hospital has raised nearly $1 million from its own employes and local hospital groups for the project. "The hospital is also near its goal of raising $2 million in public contributions."

According to Burke, the hospital plans to pay for the project not only through donations and higher patient fees, but through the sale of $22.5 million in mortgage notes.

Holy Cross, where Gov. George Wallace was treated following the 1972 assassination attempt, has been in operation for 15 years.

The facility was first envisioned in 1944 by the Allied Civic Group. The Silver Spring citizens association raised funds following World War II to purchase a 25-acre site on Forest Glen Road, according to Burke.

After the group's efforts to build a hospital proved unsuccessful, Burke said, it turned to the Congregation of the Sisters of the Holy Cross, who developed plans in 1960 for construction of the eight-story, $9-million facility.