The battlescarred Equal Rights Amendment went down to defeat to the Virginia Senate today after an opponent invoked a parliamentary maneuver to prevent Lt. Gov. Charles S. Robb from casting the key vote for its passage.

Using an unprecedented tactic, an opponent of the ERA amendment killed the measures by abstaining. The decision by state Sen. John Chichester, a Fredericksburg Republican, avoided a 20-to-20 deadlock, which would have allowed Robb, an ERA supporter, to cast the tie-breaking vote.

Chichester's abstention left the vote at 20 in favor of passage and 19 against. Under Senate rules, an absolute majority of the 40-member house, or 21 votes, is required for approval of a constitutional measure.

So those favoring passage of the ERA wound up in the ironic position of needing one more vote against their cause to give them the victory they sought.

The defeat stunned and angered ERA proponents and kept intact Virginia's record of blocking the amendment for eight consecutive years.

ERA backers had earlier lost the support of a legislator they had expected to cast the winning 21st vote. The lawmaker, Sen. Virgil A. Goode, a Democrat from Virginia's conservative Southside, today made good on his decision to switch sides and oppose the amendment. Goods had previously cited President Carter's proposed registration of women for the military draft as a major reason for the shift.

Denied his vote, the proponents had still clung to the hope of a 20-to-20 deadlock and a tie-breaking vote by Robb. But Robb's role was stolen by Chichester, who announced he would not vote because of "the best interests of my country, my state, and my constituents."

Chichester abstained from voting under Senate Rule 36, a little-used conflict of interest provision for lawmakers who have "a personal or private interest" in a bill's passage or failure. It has been used in the past by legislators with a business or other financial link to measures being voted on.

Chichester contended today he had "a personal interest" in serving his constituents and thought they could best be served "by not voting at all."

Since Senate rules also forbid questioning the motives of any action a senator may take, the ERA supporters on the floor could only complain about -- but not challenge -- Chichester's decision.

"Rule 36 will be distorted, twisted beyond all recognition if it's used to avoid a constitutional question," warned State Sen. Joseph V. Gartlan Jr. (D-Fairfax).

The proposed Equal Rights Amendment would ban discrimination on the basis of sex. The amendment has been approved by the legislatures of 35 states, three short of the 38 needed for the amendment to be added to the Constitution.

The eight senators from Northern Virginia voted for the ERA today, although state Sen. Wiley F. Mitchell Jr. (R-Alexandria) took to the floor to defend Chichester's right to abstain.

"What is sauce for the goose is sauce for the gander," said Michell, who recalled an incident two years ago in which several senators stayed in a cloakroom to avoid voting on right-to-work legislation.

Chichester's action "truly surprised" state Sen. Clive L. DuVal II (D-Fairfax), the ERA's sponsor. "I thought it was going to be a 20-20 tie, I really did, and Chuck (Robb) was going to break it," DuVal said.

Robb, whose wife, Lynda Johnson Robb, is chairman of the President's Advisory Committee for Women and an ERA supporter, had showed up on the floor with copies of a letter from former Virginia attorney general Anthony F. Troy upholding the lieutenant governor's right to vote in the event of a tie.

DuVal said that another ERA opponent Sen. Frederick P. Gray (D-Chesterfield) had earlier considered abstaining under Rule 36 "but he decided he just couldn't stomach it, having the rule misused and abused that way."

Except for the dispute over Chichester's abstention, today's floor debate was well-ordered and relatively low-key, with each side having worked out procedures and limits before hand.

For nearly two hours the proponents and opponents rehashed old arguments for and against the ERA's ratification. A packed Senate gallery looked on as 40 senators with their minds already made up listened patiently.

Although the measures came to the floor once before for debate, in 1977, losing by one vote then also, today's opponents seized on President Carter's proposal to register women for the draft as the most compelling reason to defeat the amendment.

"You cannot be for the ERA and against the drafting of women for combat," argued state Sen Eva F. Scott (R-Amelia), the Senate's first woman member and a dedicated foe of the amendment.

"Would you want you daughters or granddaughters to be on the front lines?" asked Scott, arguing that the current world crisis made that a possibility.

"It's real, gentlemen, it's real," she said.

Sen. A. Joe Canada Jr. (R-Virginia Beach) said he had abandoned his previous support of the ERA after deciding it would do more harm than good.

"Women in Virginia don't have equal rights -- they have superior rights," said Canada, who argued that existing federal and state statutes provide equal treatment with respect to employment and credit rights.

"But there's a distinction between men and women, and if you don't know that there's something wrong with you," said Canada, adding that he did not want to see any of his three daughters "in a foxhole."

Proponents, like State Sen. Edward M. Holland (D-Arlington) urged that Virginia -- as "the mother of presidents and the home of Jefferson and Patrick Henry" -- extend to women "the commitment that all men are created equal."

The harshest comments of the day came from state Sen. L. Douglas Wilder (D-Richmond), the Senate's only black, who said he was tired of having to reach back into history "several generations . . . to find people we want our children to emulate."

Noting that Virginia had balked at approving women's suffrage in 1920 and waited 32 years to ratify it after it had become law, Wilder complained that the Old Dominion also had a more recent history of "blind indifference." tThe "Commonwealth that can well believe that all men are created equal said to women, you don't even have the right to vote," Wilder complained. He admonished ERA opponents to stop living "in the mentality of the mint julep and the magnolia tree and the bonded servant."

DuVal, in particular, tried to refute predictions that approving the ERA would mean sending women to combat. He noted that the whole question of women's role in the military would be settled long before the ERA is law, and said the application of the amendment would make allowances for differences in strength and size between men and women.

Today's near-tie vote is the closest the ERA has come to approval by either house in Virginia. The measure would still have faced expected hard opposition in the House, consistently hostile to the ERA.