George Mason University left little to chance yesterday when Virginia Gov. Charles S. Robb and key state legislators came to call at the state-supported school in Fairfax County.

There was cider in wine glasses, a colorful slide show, even a carpeted step to ease the descent from the guests' air-conditioned bus. "It's the full-court press," said Senate Majority Leader Hunter B. Andrews of Hampton, who was one of the targets of the university's largesse.

The occasion was the governor's capital outlay tour, a rolling show that took the legislators from Richmond to Fairfax to Fredericksburg to hear about new buildings state agencies want to finance in the 1985-86 state budget.

In George Mason's case, that includes $14 million for the second phase of its humanities building to provide offices and classroom space, $3.9 million for a lecture center to provide larger classrooms, and $11.4 million for a science and technology center housing laboratories, offices and classrooms.

"Those requested buildings address space constraints at George Mason which are so severe that we simply have no flexibility, no margin, no way any longer even to shuffle people about," University President George W. Johnson told the lawmakers yesterday.

The space shortage is so severe that George Mason has only about half the building space called for in state guidelines, Johnson said. George Mason is so short of classroom space, he said, that the school tried to rent area movie theaters for morning classes.

The effect of his presentation was uncertain. "Capital budget tours are historically places where great sums are asked and we listen," said Sen. Dudley J. (Buzz) Emick, a Botetourt County legislator who is among George Mason's critics.

Emick said he is "enthusiastic about part of GMU," but favors educating more Northern Virginia students downstate.

Some downstate legislators like Emick have resisted the Northern Virginia school's growth -- from 4,100 full- and part-time students in 1972 to the current 15,000 -- arguing it comes at the expense of other state schools.

Del. Richard Bagley, the soon-to-retire House Appropriations chairman, said, however, "There's a lot of enthusiasm in Richmond for the growth of George Mason. There's enough to go around for everybody."