Sen. Albert Gore Jr. named Virginia Attorney General Mary Sue Terry yesterday as one of the national chairmen of his presidential campaign, and Terry, appearing with the Tennessee Democrat at a news conference in Arlington, said she would campaign for Gore throughout the country.

Terry, the first statewide Virginia Democrat to endorse a candidate in this year's presidential race, said she would begin campaigning immediately in preparation for "Super Tuesday" on March 8, when Virginia and 19 other states hold presidential primaries and caucuses.

Gore has courted Terry for months. "Her endorsement and her major role will make a tremendous difference not only in Virginia, not only in the South, but all over this country," he said at yesterday's news conference, held at the Twin Bridges Marriott.

Terry, who won the attorney general post by an overwhelming margin in 1985 and is expected to announce a bid for governor in March, said she will have to restrict travel for the Gore campaign to nights and weekends until after the legislature recesses in mid-March.

The attorney general said she decided to work for Gore, one of seven Democrats seeking the party's presidential nomination, because "the time has come to focus on one candidate." Gore "can deliver a Democratic victory, an American victory, in 1988," she added.

Observers say Terry is expected to be particularly helpful to the Gore camp in rounding up volunteers and contributors in Virginia. Terry said yesterday she also plans to meet with other state attorneys general to drum up support.

Gore has met with Democratic Virginia Gov. Gerald L. Baliles, who has said he will remain neutral in the presidential race, at least until after Super Tuesday.

For Virginia Democrats, the March 8 balloting will be the first presidential primary in the state's history in which delegates will be committed to support candidates in proportion to the number of votes they receive. Voters who choose Republican ballots will be voting in a nonbinding "beauty contest"; GOP delegates, to be chosen later, will be free to support whomever they choose.

Tipper Gore, the senator's wife, who attended yesterday's news conference, said she expects to campaign vigorously in Virginia in the coming weeks. A native of Arlington, she has several family members living in Northern Virginia.