Leaders of President Carter's Virginia campaign, citing a private poll that shows Ronald Reagan's lead in the state slipping, announced yesterday they will make "a major push" in the Washington suburbs to convince federal workers that the Republican's election would be "devastating" to civil servants.

Claiming that their data place Carter within five percentage points of Reagan, the Democratic officials said they believe the state's 12 electoral votes will be won or lost depending on how well they succeed in reaching the vast number of government workers in Northern and Tidewater Virginia.

"With stepped-up activity, we think we can put the state in the Democratic column Nov. 4," Bill Albers, Carter's recently installed Virginia state coordinator, said at a news conference at the Northern Virginia headquarters for Carter-Mondale. "Virginia is clearly winnable for the president."

Albers' assessment of Carter's chances was the most optimistic by a Democratic official in the only Southern state that the president failed to carry four years ago and came in the face of numerous predictions that Reagan is likely to carry Virginia this fall. Even well-known state Democratic officials have predicted privately that Carter's was a lost cause in the state. Other Democrats, mostly conservative local officials, have pointedly refrained from taking public roles in the poorly funded Carter campaign.

"I think it's a gasp of desperation," Robert Hausenfluck, executive director of the Virginia Reagan campaign, said yesterday. "Our Reagan efforts are very strong in both the 8th and 10th [congressional] districts [the Washington suburbs] and we have good momentum in both," he said.

But Albers said yesterday that the prospect of a close election, an infusion of organizational help from the national campaign and the tactic of tackling Reagan head-on on the civil service issue should spur more Virginia Democrats to begin working for the president. Carter himself soon will make a direct appeal to Virginia voters, targeting federal workers.

While declining to reveal details of the Virginia poll, Abers said the results had persuaded top Carter campaign officials that Virginia deserved more attention. Not only has Carter closed on Reagan, but Albers said the poll, by polister Pat Caddell, shows that support for independent John Anderson is slipping fast. Anderson, the Carter aide said, has fallen from about 30 percent to under 10 percent in Northern Virginia, where he has his strongest Virginia following.

Anderson's support and the undecided now are under 20 percent, Alber said. He refused to place figure on either Carter or Reagan's current standing, although another published poll recently placed the president six percentage points behind the GOP nominee.

The Caddell poll, said Albers, also tapped a significant anti-Reagan sentiment and showed that many previously undecided Virginia voters are choosing Carter as election day draws near. The president's new strength, Albers suggested, had prompted Reagan campaign officials to put pressure on Sen. Harry Byrd Jr., the conservative Democrat turned independent, to endorse the GOP nominee last week. "It's the first time he's ever endorsed a presidential candidate, and it was a reflection of the pressure he was under because of the close election," Albers said.

In Northern Virginia, where federal workers make up more than a third of the voters, the Carter camp plans trumpet the president's opposition to any D.C. commuter tax, his support for the Metro system and reducing air traffic and noise at National Airport. And, despite reports of widespread fear among government workers over Carter's reorganization plans, campaign officials stressed yesterday that no federal worker had lost a job because of it.

Sounding a theme that government employes in Northern Virginia and the Tidewater area can expect to hear often before Nov. 4, Albers said Reagan's first 100 days as president would be "a disaster for federal workers." Not only would Reagan abolish the departments of energy and education, created by Carter, but "on his first day, he would order a total freeze on government hiring."

Sue Hoffman, coordinator for the Carter campaign in Northern Virginia, said the decision to fight for Virginia's electoral votes has meant "a lot more campaign literature and a lot more support" from national headquarters. More people are arriving and plans are under way for a series of news conferences by local and state Democratic officials around the state, who will publicly back the president.

"I don't think it's too late at all," said Albers, who conceded that the Carter organization has been slow to gear up in the state. Albers himself just arrived in Virginia after the top Carter organizers was sidelined by illness. "You can do a lot in a short time when you have the momentum."

What has made the Virginia results even more important, Albers said, is the assessment that the Carter-Reagan contest has become a close national race in which every electoral vote must be considered.

"This election hangs on a swing of 24 electoral votes either way, and Virginia ranks 12th in the number of electoral votes," he said. "You just don't take any chances when it's that close."

Calling Carter's record "one of the best kept secrets in Virginia," Albers, who is also coordinating the Carter effort in North Carolina, said even conservative Democrats "will see the light when they compare the president with Reagan. "As Virginians begin to make their final decision on who they want to lead their country, they will look at the two futures the candidates represent," said Albers.

Republican Party officials disputed that contention yesterday and said they doubted that Northern Virginians, who supported the GOP's Gerald Ford in 1976, largely over fears of Carter's plans for the bureaucracy, would desert the party this year.