If Rosalynn Carter had any doubts about her husband's popularity among Virginia Democrats, those fears probably were allayed tonight before she said a word to a party fund-raiser here.

A straw poll taken at the door of the $50-a-plate dinner showed the president to be a runaway favorite among the state's Democrats.

The balloting showed Carter's bid for a second term had the support of 409 of the party members to 27 for his closest rival, Sen. Edward Kennedy (D-Mass.), whose Washington home is in McLean.

Party leaders tonight told the First Lady that their admittedly unscientific poll is nonetheless an accurate barometer of how strong Carter is likely to be in the state's Democratic mass meetings. Those meetings to begin later this month, will lead to sselection of Virginia's 64 delegates to the Democratic National Convention in New York in August.

But Rosalynn Carter was willing to leave nothing to chance when she took the podium at the John Marshall Hotel here to stump for Carter's reelection.

"Jimmy has a solid record of achievement," she said as her 10-minute speech was repeatedly interrupted by applause.

Citing her husband's "massive undertaking to free our nation from dependence on foreign oil" and his efforts to free the American hostages in Iran, the First Lady urged that her husband be kept in office because "we need continuity -- we haven't had a two-term president since Eisenhower."

Mrs. Carter avoided any references to the fact that Virginia was the only Southern state her husband lost in 1976 when he ran against the Republican former president Gerald R. Ford. In the past decade Virginia is the only state in the nation that has not been carried by a Democratic presidential nominee or a Democratic candidate for governor or the U.S. Senate.

Mrs. Carter was introduced by Lt. Gov. Charles S. Robb of McLean, who was introduced as "the highest ranking Democrat in Virginia."

Robb, accompanied by his two young daughters told the crowd that his wife, Lynda, the daughter of the late president Lyndon B. Johnson, could not attend the dinner because their youngest daughter was in Fairfax Hospital with what Robb described as a blood ailment. Robb said his 2-year-old daughter was doing "much, much better."

Also absent from last night's dinner were most members of the overwhelmingly Democratic General Assembly, which was edging toward adjournment four blocks away in the State Capitol.

But among those who said they would not have missed the dinner was Emily Myatt, a Democratic committee-woman from Fairfax County who has been attending such fundraisers since 1964.

Myatt, who was wearing a large green "Still For Carter Despite Everything" button, beamed when Mrs.Carter approached her table to shake hands. "I'm on the phone every day making calls for your husband," said Myatt, as Mrs. Carter smiled and glanced at the big button.

Later, Myatt told reporters she had difficulty with the Kennedy campaign. "I was very enthusiastic about John and Robert Kennedy," she said, "but I just don't think Teddy measures up."