Marc Henderson has a beautiful view, figuratively and literally, of this city's rapid transit Metrorail system.

From his ninth-floor office in the Metro-Dade County building, he can look down on Metrorail's elevated tracks, shining in the sun, and watch gleaming trains roll to and from the modern Brickell station almost a mile away.

He also can see a lower section of elevated tracks. Those are part of a smaller "Metromover" loop system scheduled to open in April. It will use one-car trains to shuttle downtown workers from Metrorail stations to substations closer to their offices.

On the inside ledge of the window providing that panoramic view, Henderson, director of public affairs for Metrorail, has placed a framed issue of the Miami Herald newspaper. Its banner headline reads:

"Metrorail rolls to rave reviews."

That paper is dated May 20, 1984. Since then, there has been little good news about the rapid transit system:

*The system has been criticized often as a "white elephant," many of whose 20 stations -- mostly in southern and northwestern Dade County -- are not near population centers.

*Less than two years after inauguration, Metrorail's operating deficit exceeds $80 million a year, and it is projected to reach $100 million this year.

*Less than 1 percent of Dade County residents use the air-conditioned Metrorail, which whooshes along at speeds of up to 70 miles an hour.

Metrorail's critics extend all the way from the Herald to the White House.

In a speech to local government leaders in Washington last March, President Reagan called the federal subsidy for the Metrorail a "$1 billion mistake." He said ridership was so low that "it would have been cheaper to buy everyone a limousine."

Metrorail's ridership problems are somewhat unusual compared with other cities' rapid-transit systems. Metrorail draws well among whites and poorly among minorities. Fares are $1.

Henderson said many blacks who long have used public transportation have voiced a preference for buses and cabs, and they expressed fears of riding the Metrorail because it is entirely elevated.

"Our ridership is improving," Henderson said, though he admitted, "Obviously, it's not where we would like it."

On the optimistic side, he pointed out that the current 23,000 average daily ridership is triple the 7,000 in the system's first months. On the other hand, consultants who helped sell the system to Miami voters projected a daily figure of 200,000 after it is fully operational in April.

The only day it achieved that figure was opening day 1984, when throngs tried out the new system. The $1 fare was waived that day. The next highest ridership days -- 35,000 last Sept. 9 and 40,000 the following day -- were because of fans flocking to Bruce Springsteen concerts in the Orange Bowl.

Critics note that there is no station within walking distance of the Orange Bowl (shuttle buses cover the 1-mile distance) and that, although the line heads due west toward the airport, it suddenly curves north 3 miles away from it.

As 1986 begins, Metrorail officials face a difficult double task: They have to do surveys to find out why so many Miamians aren't using the system. They also have to ask those people to pay more taxes to support Metrorail.

"We need a dedicated source of funding," Henderson said. "Mass transit systems need that, and we don't have it."

The preferred source is a 1-cent increase in the state sales tax in Dade County. A countywide referendum on the proposal will be held next November. The tax increase, which would produce $118 million, already has produced opposition.

Richard Friedman, an attorney, a leading critic of Metrorail and leader of a successful campaign in 1978 that blocked a similar sales tax increase for the first stage of the system, said: "They're not going to pass this tax because I'm going to fight them and beat them again. "Why should all of the people pay a tax so that a handful of the people can take a train to nowhere?"

Realizing that considerable help is needed to pass a sales tax increase, Metrorail supporters on the county commission are inviting a "blue ribbon" committee of business leaders to evaluate the Metro-Dade public transportation system -- Metrorail, buses and the imminent Metromover.

Although the committee has not yet received instructions from the full county commission, its membership has been named.

Chairman Frank Callahan, who is also chairman of the South Florida Regional Planning Council, said candidly: "I think the commission hopes it will get some tacit endorsement of the sales tax from us. But I think we have a lot of questions about whether and where waste can be whittled out of this system, and if and where salaries are too high. I would like to take a hard look at every component of that $100 million deficit."