The Rev. Michael Bazan looked uncomfortable at rest, sitting ramrod-straight in his office with his Roman collar undone.

It was Thursday, only hours before the pastor of St. John the Evangelist parish in Warrenton was to begin a week-long vacation in his native upstate New York, and there still were things to be done at work.

"It's a busy day," he said with a weary smile. And the days for Bazan and his associate pastor, the Rev. John Riley, will only get busier if current trends continue.

With a growth in parishioners that outpaces the rate of population growth in the county and the region in general, St. John received approval last month from the Roman Catholic Diocese of Arlington to begin raising $2.5 million for an addition to its 35-year-old church.

"The parish just keeps growing and growing and growing," Bazan said, with a hint of amazement in his voice. "It never stops."

The experience of St. John is being repeated in parishes across the diocese, particularly in areas such as Prince William and Loudoun counties, officials said. In the last four years, the diocese has acquired four parcels for potential parish sites in those counties and Stafford County and is considering purchasing two others, said Thomas Fadoul, general counsel for the diocese.

Other denominations in the fast-growing region have experienced similar pressures to build and expand. But, according to diocesan officials, the number of Catholics in the diocese is growing faster than the rest of the population. Officials predict that the percentage of Catholics in the diocese, which comprises 21 Virginia counties, will increase from the current 16 percent to 21 percent in 20 years.

Fadoul attributed the growth projections to new jobs that attract people from more traditionally Catholic areas, such as the Northeast and Midwest, as well as an increase in ethnically Hispanic and Asian populations that tend to be more Catholic.

"It's nice to be in a place that is growing and vibrant," said the Rev. Robert Rippy, aide to newly installed Bishop of Arlington Paul S. Loverde.

But with this growth has come complications, such as space crunches and a need for fund-raising. In St. John's case, Bazan said, "a lot of this planning should have been done 20 years ago. They saw that this was coming. . . . Now, we're kind of doing things backwards."

At St. Francis de Sales Church in Purcellville, Monsignor Thomas J. Cassidy said standing-room-only Masses will necessitate adding a Sunday service.

"Well, you've heard of the proverbial mushroom. We're growing in leaps and bounds," Cassidy said.

In 1992, with membership around 200, its small church on Main Street was replaced by a new one on 10 acres with a capacity of 550. By 1997, when the diocese took over the administration of the parish from the Franciscan religious order, there were 836 registered families, Cassidy said. Now, he said, there are 1,060.

There is no parochial school associated with St. Francis. So religion classes for school-age students are being held at Loudoun Valley High School. "We're space-poor right now," Cassidy said.

He said that parents have approached him to create a school but that requires money, which could be hard to come by.

"We're still paying off the debt on what we've got," he said.

At St. John's in Warrenton, Mass already is crowded. This year, for the first time, Easter services were held in the Fauquier High School auditorium.

"It was the only place that could accommodate it," Bazan said.

He said the same will be done for Christmas services. The parish has grown from 1,500 registered families in 1992 to more than 1,800 today, with an estimated 4,000 people attending Mass each weekend.

"We have to have two priests for Reconciliation on Saturday, where we used to be okay with just one," Bazan said, referring to the rite otherwise known as confession.

Bazan said the new arrivals come from larger parishes that provide many programs such as youth groups, Bible study and outreach to the poor.

"They expect the same kind of service they got at their previous parish," he said.

To accommodate these new programs, Bazan authorized the hiring of a business manager in 1996, a development director in 1997 and a social justice programs coordinator this year.

St. John, the largest church of any denomination in Fauquier County, is facing particular pressure because it is the only Catholic parish between Warrenton and All Saints Church in Manassas, where its 20,000 parishioners make one of the largest churches of any denomination in the state.

There, nine weekend Masses are held, seven of them standing room only, said the pastor, the Rev. Paul Verrecchia. The parish recently completed a new 35,000-square-foot school and is considering a fund-raising campaign of its own for a new church.

Verrecchia said he and three associate pastors have sought to involve parishioners in the life of the church so the large numbers don't serve as a discouragement.

"You can do great things with numbers," he said. "It's a matter of making sure everybody internally doesn't get lost."

To relieve some of the pressure on All Saints, the diocese has purchased property in Gainesville, in Prince William, and is considering property near Bealeton, along the Route 28 corridor. Two sites in Loudoun and one in southern Stafford have been acquired but have not received final approval from Loverde as church sites, Fadoul said.

Some parishioners at St. John the Apostle Church in Leesburg were upset earlier this year when the diocese sold land that could have been used to expand the church. Rippy said Loudoun, which already has five Catholic churches, will need the two new ones that are nearing final approval by the bishop.

"It is a growth area," he said, "and that is a place where we are going to have to accommodate needs."