Virginia Lt. Gov. Charles S. Robb sounded an election-year call for Democratic party unity tonight as delegates to the state convention here prepared for a weekend battle over choice party leadership posts.

Mindful of festering tensions between conservative and liberal Democrats, Robb alluded to party warfare even as he delivered an up-beat keynote address about the party's state and national strength and appeal.

"Now I know what some of you are going though and I know that emotions are running high," said the man considered the likely Democratic candidate for governor in 1981.

"But when all is said and done, we must come back -- each and every one of us -- to the basic commitment to our party because the people of this commonwealth and this nation are depending on us for leadership," Robb told a Richmond Coliseum crowd of more than 4,500.

Despite Robb's assurance that a revitalized Democratic Party is ready to take on Republicans, the contests getting the most attention tonight involve intra-party disputes over convention representation and an upcoming fight for Virginia's four seats on the Democratic National Committee.

Supporters of President Carter, who boast the overwhelming majority of convention delegates here, easily turned aside an angry challenge by Kennedy backers who sought to seat additional delegates from the Richmond-Chesterfield area. Carter is expected to get 59 of Virginia's 64 presidential nominating delegates to the national convention this summer.

But the election Saturday for national committee seats will be more rancourus. Many liberals in the party have rallied around incumbents George C. Rawlings and Ruth Harvey Charity, considered to be targets of a purge by conservative and moderate forces in the party.

Some 24 party leaders have endorsed a slate of four moderate candidates, prompting former Lt. Gov. Henry Howell to warn that liberals may not support party candidates this year or next if Rawlings and Charity are ousted.

"You win with Democrats by standing up and talking like Democrats," Rawlings, the 58-year-old Fredericksburg attorney and long-time party activist, said today.

A Kennedy supporter, he argued that the party should keep putting up Democratic candidates who provide a contrast to Republicans and who can also attract liberal-minded independents. But he promised to work for any and all party nominees in coming elections.

Other party officials have complained that the Rawlings camp has isolated itself from the party by refusing to work for Democratic candidates who they feel are not sufficiently progressive.

The real concern at this convention, according to several party officials, is that the so-called purge dispute will hurt the Democratic candidates in November. Virginia was the only southern state to back Gerald Ford four years ago, and its voters have not been kind to Democrats in recent state-wide races.

"George is a fine person, but I just feel it's time for new leadership," Dottie Schick, who chairs Fairfax County's Democratic Committee, argued today.

As one of 24 prominent Democrats to sign a letter backing four other committee candidates, Schick said anti-Rawlings sentiment was directed more against his personality and style of leadership than his liberal politics. m

"I think it's time we got away from the term 'Howell people,'" said Schick in a reference to ardent supporters of former Lt. Gov. Howell, who narrowly missed being elected governor in the early 1970s.

Rawlings said. "We talk about being Howell Democrats because we love him, and it's an easy way to identify people. Henry's the first to recognize he's not likely to run for anything again, but it doesn't mean he and the rest of us aren't concerned about the way the party is going."

Although Rawlings has appraised his own re-election chances at 50-50, he picked up a much needed boost today by getting the public support of Northern Virginia Democratic Rep. Herbert E. Harris. A Harris letter was circulated by Rawlings supporters in preparation for the committee election showdown Saturday.

Although the endorsement angered some Harris supporters who wanted the Eighth District congressman to stay out of the fray, an aide to Harris said he wrote the letter at Rawlings' request after deciding, "you don't dump your friends."

The party's liberal faction also lost its attempt to have the party organization choose its officers in a presidential election year when interest in Democratic politics is usually higher. Instead, the convention voted to begin holding the election of party officials in gubernatorial years.

This means that Portsmouth mayor Richard Davis, who was reelected state chairman tonight, will be up for reelection again in 1981 along with other party officers.