Jack Kvancz, George Mason University's athletic director, stayed late at the office Sunday night, waiting for the phone call for the Patriots' first postseason basketball tournament appearance. Then he had to make arrangements to get the team to Beaumont, Tex., to play Lamar Thursday night in the first round of the National Invitation Tournament.

The phone kept ringing, and the question basically was the same: "Did Mason get a bid?" About midnight, Kvancz finally got in touch with Coach Joe Harrington, who was on the road recruiting. "Your team's in," Kvancz told his coach. "That's good for the school. But I'm going to Texas with my golf clubs. I owe it to myself."

The phones kept ringing yesterday, with congratulations on Mason's breakthrough. Indeed, when George Johnson became president of the then-very-small commuter school in 1978, he said he wanted to build a national identity through a classy, orderly athletic program. The 1978-79 season was Mason's first in Division I, and Harrington, a former player and assistant coach at Maryland, became the Patriots' first fulltime coach two years later.

Now, almost 17,000 students are enrolled at Mason; the university opened the 10,000-seat Patriot Center this season, and the basketball team for the first time gained its conference tournament final and a postseason tournament bid.

As Harrington said, "Two years ago, we were 21-7 and didn't go anywhere. This year, we're 19-11 and eight of our losses were to NCAA tournament teams . . . Our program has really improved, and it's getting better all the time. I'm not going to let it stop. We're not a Big East school or an ACC school. We're a basketball team that's really improving. Gosh, it takes time."

The one thing Johnson wanted to do was build a strong foundation and do it honestly. No quick fixes or overnight sensations. From all indications, the Patriots have done it with hard work and no shortcuts. Like many schools on George Mason's level, the team is a good big man away from being a top 20 contender. Players such as Rob Rose, Ricky Wilson, Kenny Sanders and Earl Moore could play in almost any Division I program.

"I want to see it continue to evolve," Johnson said. "It's right on target. Joe has done a great job. I like the style, the tone of the program. I like the kind of perspective in which Kvancz keeps the program."

Harrington sees both the tangible and intangible benefits of this season.

The tangibles: "Just the publicity and being able to put something back for the money that's been spent here on basketball. It's also a reward for our players."

The intangibles: "Bringing attention to the school in a positive way. It will help next year when it becomes time for season-ticket sales (300 in 1984-85, 1,200 this season, a goal of 2,000 next season). It will help us in the future on the NITs and NCAAs by playing in a postseason tournament."

Harrington said that moving into Patriot Center, a fairly plush campus facility run by professional arena managers, "has made a big difference, just in the attention it has brought to the school . . . It's really changed this program -- our image and the whole thing. It's really made a difference."

Already, Harrington is close to getting a commitment from a big man, 6-foot-10 1/2 Henri Abrams of Mackin High School in the District. He would be the tallest player ever signed by Mason.

When the Patriots go to Texas for Thursday's 8 p.m. game, they will be facing a team with size and a basketball reputation. The Cardinals (18-11) missed winning 20 games for the first time in eight years. Lamar's home record the past nine seasons is 113-11, but the Cardinals are 24-6 the past two seasons since moving into the 10,080-seat Montagne Center on campus.

Coach Pat Foster probably will start a front line that includes 6-11 Greg Anderson (11.9 points, six rebounds per game) and 6-9 Anthony Todd (15.5 points, 6.9 rebounds). Reserve James Gulley, who is 6-8 and weighs 278 pounds, averages 13.9 points and 5.7 rebounds.

Johnson, the university president and an ardent fan, will not be going to Beaumont to see the game, even though Lamar's president is an old friend. He has a previous commitment -- to attend a reception honoring Manuel Johnson, a former faculty member who is a new governor of the Federal Reserve Board. "That's keeping the proper perspective for somebody who's such a big a fan as I am," Johnson said.