It was billed as an historic event and a golden opportunity for the Democrats who control Virginia's legislature to assert their power over Republican Gov. John N. Dalton. Instead, the General Assembly's first veto-override session fizzled today as lawmakers conceded they were unable to muster the votes to overturn any of the governor's vetoes.

"It does look a bit like we labored over a mountain and brought forth a mole hill," said Del. Mary A. Marshall, an Arlington Democrat.

After counting noses in both legislative houses, the sponsors of four bills that had passed the assembly's 1981 session but had been vetoed by Dalton last week did not even bother to bring their measures up for a vote.

Black legislators, working for a fifth vetoed bill to establish the Jan. 15 birthday of slain civil rights leader Martin Luther King Jr. as a state holiday, had the bill put off until tomorrow. But they, too, acknowledged they appeared to lack the votes for an override.

Two of the bills that died today would have authorized state Medicaid funding for abortions in pregnancies resulting from rape or incest or in cases of gross fetal deformity. Supporters of the measures said they had the bills stricken from the House of Delegates calendar in part because they did not want to force colleagues to vote again on a controversial matter that could become an issue when the delegates run for reelection this fall.

"No one wants to gratuitously embarrass their colleagues by making them vote on a bill that is going to lose anyway," said Williamsburg Democrat George Grayson.

Other lawmakers said the override session's failure was a tribute to the power -- and mystique -- of the governor's office, which under the Virginia Constitution is one of the nation's strongest state chief executives.

"The votes aren't there to override vetoes and they have never been there in this legislature," said Fairfax Del. Vincent F. Callahan, Northern Virginia's senior Republican lawmaker. "The aura of the governor is intimidating in this state and not too many people are willing to get into a big fight with him regardless of whether he's a Democrat or Republican."

Callahan said the governor was so certain he would win on the veto questions that when he and other Republican legislative leaders visited Dalton yesterday, the subject never came up. Said Dalton press spokesman Charles Davis today: "The governor has always been fairly confident his actions would be sustained."

Part of the governor's power stems from the fact that for most of this century, Democrats controlled both the legislature and the Governor's Mansion and legislators were accustomed to following the governor's lead. Even though the last three governors have been Republicans, the tradition lives on.

"These guys have been culturally conditioned to work with the governor, so they continue to do so," said Del. Lewis Fickett (D-Fredericksburg), who today withdrew his bill enhancing teachers' grievance rights after the governor recommended a series of amendments Fickett said would gut the measure. "It was a simple motherhood bill and I couldn't get the leadership to support me," Fickett said.

Two years ago, when the assembly passed -- and state voters approved -- a constitutional amendment authorizing the veto sessions, lawmakers argued the sessions were needed to give them the power to overrule the governor. But some said that today's failure to override might actually enhance the governor's power.

Other argued that even though no vetoes were overridden, Dalton and future governors have been put on notice that they can no longer ignore legislators in deciding on vetoes. "The very fact that we had a veto session makes a real difference," said House Majority Leader Thomas Moss. The Democratic legislator said he believed Dalton signed some bills this year he otherwise might have killed to avoid risking a veto fight.

Supporters of the bills funding abortions said they had known long before today they lacked the two-thirds votes to override Dalton. The bills' chief sponsor, Del. Samuel Glasscock (D-Suffolk), accused the governor of a "lack of tolerance for the views of others and a lack of concern for people who need help" in vetoing the bills. Glasscock predicted similar legislation would be passed and signed by Dalton's successor next year.

But one of the bills' prime opponents, television evangelist Jerry Falwell, founder of the Moral Majority religious lobby, hailed the governor's vetoes and sent his supporters form letters to forward to Dalton. "The people of Virginia, born and unborn, owe you have given to the Commonwealth these last four years," the form letter began. "In a day when public service is looked on by some with suspicion, I am proud to have had you serve as the chief executive of our great Commonwealth."

Because today's veto session took less than 90 minutes, most of the 140 lawmakers here spent most of the day jockeying over redistricting proposals. While House members appeared to be closer to agreeing on a reapportionment plan for their districts, a Senate plan endorsed by that chamber's leadership ran into unexpectedly strong opposition and was returned to the committee that had authored it.