In 1981, candidate Charles S. Robb came out in favor of registering voters by mail--an idea long advocated by black and liberal groups as a way of opening up Virginia's historically restricted electorate.

In 1982, two days after he took office, Gov. Robb had a better idea. He told a joint session of the General Assembly he would propose legislation to allow state employes -- at the Department of Motor Vehicles, for instance -- to participate in the voter registration effort.

In 1983, when the legislature was considering amendments to the state constitution to do either one of those two things -- registration by mail or by state agencies, Robb backed off both, saying he preferred to wait until 1984 for any comprehensive reform of Virginia's voter registration system.

Last month, Robb came out with a decision on voter registration. His proposal? A 17-member, bipartisan task force that is expected to make its final report in 18 months -- in time for the legislative session in 1985, Robb's last year in office.

In a state that continues to rank near last in the country in the percentage of eligible citizens registered to vote, Robb's caution on this issue has baffled some supporters. Why, they ask, does a governor need an 18-month study to decide how to honor his own campaign pledge?

"I'm disappointed he hasn't taken a stronger stance early in his administration," said Del. William Robinson (D-Norfolk), whose bills to allow registration by mail or state employes died last year without Robb's support. "I don't know why he has modified his position -- and I am being charitable when I say that."

Others doubt that the task force, to be headed by Lt. Gov. Richard J. Davis and made up of representatives from the NAACP and the American Civil Liberties Union as well as Republicans and businessmen, will be able to agree on the kind of reforms they had expected from Robb.

"I just question whether a group that diverse can give us -- or will give us -- that which is most needed in Virginia," said Sen. L. Douglas Wilder (D-Richmond), Robb's most strategic black political ally and another sponsor of last year's doomed voting changes. "It's going to be interesting to see what does come down and what the governor gets behind. We don't need placebos or window dressing."

No one questions Robb's commitment to an open electorate. In Virginia, where government moves slowly, the appointment of a task force is hailed by some as a sign of concern for a long-neglected problem. There is also a recognition that Robb will need help in selling any significant changes to a legislature that has displayed a fundamental distrust of reaching out to new voters.

"There are those who say there is no need for a study, and to a certain extent I agree," said task force member Michael Brown of the NAACP. "But to have an official stance, to say this is one appointed by the governor, gives credence to the problems. We have to educate the public, but we also have to educate members of the legislature."

Roughly 58 percent of Virginia's eligible voters -- 2.2 million individuals -- are registered. With or without the help of the task force, Sue Fitz-Hugh, secretary to the State Board of Elections and a Robb appointee, has set a goal to increase that by another 10 percent in time for the 1984 presidential elections.

This fall, a new jingle will hit Virginia's airwaves, urging people to get out and register; the message has gone out from Richmond that local registrars are supposed to encourage, not discourage, registration drives. Those efforts are well under way in Northern Virginia. Because of a state law that puts local electoral boards in control of the party that holds the governor's office, 40 of the state's 136 local registrars' office changed hands this year, in some cases bringing a new philosophy about voting.

The chances of starting the long, arduous process of amending Virginia's constitution -- either to take out the current requirement that people register "in person" or to lift the ban against registration by salaried government employes -- are slim in 1984. (Before a constitutional amendment can be put before the voters, it must be voted on by the legislature twice--once before, once after an election year. After this fall, the next legislative election will be in 1985.)

Robb's solution is in many ways typical of his "consensus-building" style. "He's a very practical governor," said former lieutenant governor Henry E. Howell of Norfolk, the populist who two years ago led a march to the state Capitol to press Robb on his campaign pledge for mail registration. "That is the Robb way . . . . It's not the Howell way, but then I've never been elected governor."