The suburban Washington legislative delegations, which will play a pivotal role in the success or failure of the D.C. voting rights amendment in the Maryland General Assembly, have shifted solidly in favor of the measure over the last week.

A survey of Montgomery and Prince George's legislators today revealed that at least 75 percent of them will support the amendment to give the District of Columbia two voting U.S. senators and at least one congressman, despite a persistent fear that it might eventually lead to a suburban commuter tax.

The strong support of these two delegaitons, coupled with indications that the amendment will receive favorable reports from House and Senate committees here later this week, has encouraged ratification proponents who only one week ago were having difficulty finding support.

After furiously roaming State House halls since last and buttonholing their colleagues, sponsors of the amendment now say they have enough support to carry the measure when it reaches the floor of both houses.

"We're right on the nose," said Sen. Clarence M. Mitchell Ill. one of the Senate sponsors. "I've got 24 hard commitments (the minimum constitutional majority) and four more leaning my way. Now it's just a matter of nailing it down and not losing ground."

The amendment has lumped together an unusual coterie of sponsors. Mitchell, a savvy black Baltimore politician, has rallied the legislature's Black Caucus to work behind the secnes for the measure, while he shuttles back and forth to committee hearings with the other two chief sponsors -- Sen. S. Frank Shore, a Democrat from Montgomery, and Del. Charles S. Blumenthal, the Prince George's Democrat who enjoys needling his colleagues with incessant "points of order."

The three proponents regularly appear at the committee meetings, arriving early to organize their long procession of witnesses. Then, they take turns asking their colleagues to help make Maryland the fourth state to ratify the voting rights bill.

As a neighboring state, Maryland is considered an important test for ratification advocates. to become effective, the amendment must be approved by 38 state legislatures within seven years of last summer's approval by Congress. So far, four states have rejevted the measure and one state has postponed action.

The success of the amendment here so far is due in large part to the strategy of its sponsors. They realized from the start the measure would be of little interest to legislators from outside the Washington area, and scheduled hearings before rural and Baltimore area legislators became preoccupied with local projects.

The proponents also owe a lot to D.C. Del. Walter Fauntroy, who has impressed Maryland lawmakers with his philosophical and practical arguments in favor of ratification. "The guy made a believer out of me," Sen. Victor L. Crawford (D-Montgomery) said after a committee hearing last week. "He's right when he says those people deserve representation."

Fauntory was equally persuasive today when he testified bofore the House Ocmmittee on Constitutional and Administrative Law. One member of that committee, freshman Del. Francis W. White (D-Prince Goeroge's) entered the hearing saying he would vote against the amendment and left an hour later saying he would "support it wholeheartedly."

"My concern was that the District should seek statehood rather than just full voting rights," said White. "Fauntory convinced me that statehood was not a feasible alternative because 60 percent of their property is untaxable."

White is one of at least 10 Prince George's delegates who over the last week have shifted from the opposition or undecided ranks.

In the county's Senate delegation, however, the picture is different, with five of the eight senators saying they will vote against ratification. These five senators have been most vocal in their fear that the District, when it gets full voting powers, will persuade Congress to impose a commuter tax on Suburban Marylanders and Virginians who work in the city.

"I've gotten an awful lot of mail from my constituents who are afraid of the commuter tax," said Sen. Arthur Dorman, "Unless I get a groundswell of letters the other way, I'm voting against it."

Sen. Thomas V. (Mike) Miller, from the 28th district in southern Prince George's said he considered his opposition a "courageous political stance." He explained:

"The supporters are going to make a racial issue out of it. They'll say I'm racist, even though that's not true. To tell you the truth, the only reason I even considered supporting it was my fear that I'd be called antiblack."

No single issue has taken as much time or as much thought for many Montgomery legislators as the cosntroversial amendment. Del. Constance A. Morella, a Bethesda Recpublican, said she has received such mixed signals from her constituents that she decided to conduct her own poll of 3,000 people in her district.

If the amendment fails to pass quickly once it reaches the floor, supporters believe, it could become a lightning rod for vote trading. At least one legislator from Montgomery realizes the potentila for such bartering and decided to withhold judgment for the time being.

"There are a lot of other people in the state that wnat the D.C. rights bill," said Del. Judy Toth (D-Montgomery). "There are a lot of things we need in Montgomery, like more funding for Metro. We'll see what we can get for it (support of the amendment."