The yellow chartered buses started arriving at 9:15 this morning, disgorging dozens of frail, bespectacled men and women. By 9:30, the Senate Finance Committee hearing room was overflowing with grim-faced senior citizens. And still the buses kept coming.

"Ooooh, boy! Here they come. They think they're going to intimidate us," muttered committee chairman Melvin Steinberg (D-Baltimore County) through tight lips as his secretary gave him updates on the growing throng.

The occasion was a hearing on what has grown into the issue of the year for the aged: a bill that would create a full-fledged Department on Aging out of the office that now addresses the elderly's needs in Maryland.

The 200 men and women who braved subfreezing temperatures to come here today from 17 counties and the city of Baltimore insisted that the measure literally represents the difference between life and death for old people, who cannot find their way through the bureaucracy that is supposed to help them.

But several leading legislators say they fear the push for a department represents a "hoax" that would do nothing more than expand the state bureaucracy and add $9,000 to the salary of Dr. Matthew Tayback, the director of Maryland's Office on Aging, who would be elevated to the status of department secretary.

"I'm not about to pull the wool over the eyes of these citizens who have been told the department is going to solve all their problems. It's a farce and it's a shame," Steinberg said angrily after the four-hour hearing in which septuagenarians and octogenarians took the microphone to make impassioned pleas for the bill. "Dr. Tayback wanted this bill and he has established a Frankenstein."

Steinberg and several other senators argued to the proponents of the bill that they have no evidence that a new department will help the elderly, particularly at a time of fiscal crisis, when all existing departments have had to make cutbacks.

Even Tayback, who was believed to support the bill, spoke against it, albeit half-heartedly, explaining that he was speaking for Gov. Harry Hughes and not as an individual. Hughes, he said, believes that services to the elderly can be improved under the present system.

But this did little to pacify the elderly listeners, who sat attentively in the audience, occasionally hissing under their breath at the senators. As they left, they variously called the committee "mean," "callous," and chartered bus: "They [the senators] obviously don't think they're ever going to get old."

The bill will probably be sent to a summer study session rather than to the Senate floor, several committee members said. But given the huge turnout today and elderly voters' reputation for similarly high turnouts on election day, several legislators expressed surprise at Steinberg's firm stand. By contrast, Anne Arundel County Executive Robert Pascal, a leading Republican prospect for the governor's race in 1982, showed up to support the bill, to resounding applause from the audience.

And, 29 senators signed up to co-sponsor the bill with its prime sponsor Sen. Margaret Schweinhaut (D-Montgomery County), the Senate's senior member at 75 and a longstanding advocate whose record on elderly causes gives her a status here akin to that held by Florida's Claude Pepper in Congress.

Schweinhaut, her white hair glistening under the klieg lights, cut a commanding figure at the witness table as she pointed her finger at the committee and warned: "Let me tell you this. Older people have only so many years left to live. If you're going to leave them in the quagmire of the bureaucracy, they'll die before they ever reach the programs."