When State Sen. Nathan H. Miller (R-Rockingham) left Richmond at 7:20 this morning on a flight for Atlanta, the last slim hope of ratifying the Equal Rights Amendment in Virginia went with him.

Miller, a conservative senator from the Shenandoah Valley, has long been an opponent of the controversial constitutional amendment banning sex discrimination. But Miller's absence from the Senate today was far more effective in killing the measure than his "no" vote could have been.

It left the Senate to vote 20 to 19 in favor of the measure--one vote short of the constitutional majority needed to send the ERA to the House, and lacking the tie vote that would have brought an affirmative tie-breaking vote from Democratic Lt. Gov. Richard J. Davis.

Today's Senate action marked an emotional end to a nine-year struggle toward ratification here, and leaves ERA supporters still three states short of the 38 needed before the amendment's ratification deadline of June 30. "I don't think the women of Virginia will ever forget what they did here today," said Lulu K. Meese, an ERA organizer who was among the crowd of supporters and opponents packing the Senate gallery for the debate. "We will just have to go to work in other states."

Still, many ERA supporters had conceded that today's Senate appeal was at best a long shot. The rights amendment already had been roundly defeated this month in a House committee, and another procedural move designed to save it had been killed 62 to 35 on the House floor.

As Virginia First Lady Lynda Bird Robb watched from the gallery in dismay and ERA lobbyist Marianne Fowler fought back tears, the Senate today turned in a vote that was virtually identical to its last floor vote to kill ERA, cast in 1980. Only the name of the nonvoting ERA opponent was different. Last time Sen. John Chichester (R-Fredericksburg) had abstained, claiming conflict of interest, while this year Miller, a Shenandoah Valley lawyer, went to Atlanta to handle a private legal case.

"I can assure you that when he scheduled the case he didn't know the ERA was coming up the same day," said Marsha Shenk, Miller's legislative assistant.

The final defeat of the ERA in Virginia seems to mark a personal setback for Democratic Gov. Charles S. Robb, who had aggressively lobbied two key senators on its behalf and had helped ERA leaders Sen. Clive L. DuVal and Del. Dorothy McDiarmid (both D-Fairfax) plan their strategy. Robb had met repeatedly with Sens. Willard J. Moody (D-Portsmouth) and Daniel W. Bird Jr. (D-Wythe) over the past weeks after proponents reported that polls seemed to indicate their constituents favored the measure. But both men declined to change their votes.

"In this case, there was only so much he could do or anybody could do to change positions that have been campaigned on for years," said Robb press secretary George Stoddart. "You plan the most effective strategy you can, and if it works, great. If it doesn't, it doesn't."

Moody and Bird both rejected suggestions that their "no" votes could be read as an indication of the new governor's lack of lobbying power. "I don't see it as a slap at the governor," said Bird, who was visited at his seat by a host of ERA opponents before the final vote was taken. "I had no personal thing against it . . . but I had made a commitment in my district."

Today's ERA debate followed a pattern that has become almost a ritual in Virginia: Supporters argued that it was "a matter of simple justice" to guarantee women equal rights under the law, while opponents claimed the proposed amendment to the U.S. Constitution would open the door to homosexual marriages, sexually integrated public restrooms and unwanted federal intervention in state affairs.

But in the end, the 40-minute debate had little influence over the outcome. "Everybody had made up their minds years ago," said one senator. "There was no way they were going to change now."