Bull Run Mountain lazed in rosy mist on the western horizon. The morning sun crept slowly over a distant Capitol. And a somnambulent crew of government workers, secretaries and mid-level executives climbed the steps of the Z-28 express bus to a new day.

At the end of Metro's suburban reaches, far from Washington or even 7-Elevens, this was the morning after The Big Debate and these Chantilly straphangers would render their own verdict. What would it be?

Yawn.

Yesterday morning, a winning majority could have swung on a good cup of coffee, such were the convictions of these early Fairfax County risers.

"I fell asleep," said Sally Virgulak about the nationally televised Carter-Reagan duel the night before. "I'm really embarrassed to say it, but I did."

This is Reagan country, out here where rush hour starts at cock's crow. A quick reading of the Z-28 confirmed as much. In many cases, it is a grudging support, riding on the same kind of enthusiasm these voters bring each morning to their 90-minute commute to the Pentagon, Crystal City and the Federal Triangle.

Most say they watched the debate, or at least the parts for which they were awake. Nearly all were unimpressed.

"It was a waste of time," said one rider. "It's really difficult to make any kind of decision," said another, "because they all keep hiding what they really believe."

But, yes, some minds were changed. "Before I was sort of leaning toward Reagan, said Air Force Maj. Charles Shidisky, on his way to the Pentagon. "And in a way, I was kind of hoping the debate would change my mind. There are some serious questions about what any one man can do without the power of the presidency already behind him. But now, I don't think Reagan will do any better or any worse than Carter. So I guess I'm just voting for a change."

Few riders on the bus yesterday moringing would admit to wanting to live on the county's western edge, where the march of town houses and civilization moves steadily across the rolling landscape. Many of them are new arrivals; those for whom housing is a choice born of a sinking feeling in the bank balance.

The economy has not won Carter many votes here.

"Carter's had five economic policies in the last six months," groused Howard Williams, a technical instructor at MCI Telecommunications in the District of Columbia. "He's just reacting to situations, rather than resolving them."

"I went into the debates looking for very specific answers to very specific questions," said Shidisky, "like, how you're going to be able to afford to put food on the table for your family, and how you're going to be able to afford a house."

He was disappointed.

Bill Bourland, sitting in his three-piece suit a few seats back of the driver, moved to Chantilly recently from North Carolina. An attorney for the Justice Department, he cites his own experience in the government as the reason he is siding with Reagan.

"I see so much waste in government," he said. "It's sometimes almost sickening. I see [government workers] every day and I don't know what they do. And I don't think anyone else knows what they do. With Reagan, I can spend my own money, rather than the government spending it for me."

Some were impressed by Reagan's carriage at the lectern. "Reagan looked a lot stronger, a lot calmer, a lot more presidential," Williams said.

Despite Reagan's polished television demeanor, a few on the Z-28 distrust him, even though they would be happier with an alternative to the Democratic incumbent. "I trust his [Reagan's] instincts," said one, "but the fact he's close to the Oval Office frightens me. He doesn't think in concepts or ideas and he doesn't talk that way. I'm an Anderson supporter, but I really see a vote for Anderson taking a vote away from Carter."

Carter can count on a few votes among the Z-28 regulars, though equally as unenthusiastic. Their support is loaded with qualifiers, moans about his failure to address and answer debate questions directly, and sometimes aimed more at specific issues on which they cannot agree with the Republican challenger.

"I don't believe one man makes much difference," said 28-year-old mortgage banker Mark Roadley. "I would prefer to vote for the man, rather than the party. But the man doesn't seem to be that outstanding. I hadn't decided until last night who I would vote for. It's Carter, because I think the policies he started are good."

Sally Virgulak, a young executive secretary at the American Council of Independent Laboratories who sat squeezed into a corner by her stunningly obese bench partner, will just be glad when it's all over.

"Election, election, election. That's all I've been hearing for the last six months." Virgulak, who says she is casting her vote for Carter because of Reagan's opposition to abortion and the Equal Rights Amendment, said her husband is driving her bananas with his constant talk of the vote.

"He thought Carter made a complete fool of himself and he was really disappointed," she said. "So now he's going to vote for Regan. Maybe then we can talk about 'us.'"