Gov. Michael S. Dukakis scored runaway victories over the Rev. Jesse Jackson in Nebraska and West Virginia primaries yesterday, continuing his march toward the Democratic presidential nomination.

The landslide triumphs left Dukuakis with three-quarters of the delegates needed to lay claim to the nomination, buttressing his image as the party's 1988 choice in all but name.

With 56 percent of Nebraska's precincts reporting, it was Dukakis 65 percent, Jackson 25 percent. Dukakis was leading for 18 delegates, to 7 for his rival.

With 15 percent of West Virginia's precincts reporting in a slow count, Dukakis was gaining 80 percent of the vote to 14 percent for Jackson.

Even as his defeats were sealed by the voters, Jackson was looking ahead to next week's primary in Oregon as well as the final showdown June 7 in California. Campaigning in Portland, he said, "We know the people of Oregon are an independent-thinking people. We expect a tremendous response..."

Vice President George Bush won the West Virginia primary with 89 percent, his customary, uncontested landslide.

Nebraska was something of a different story. Bush was gaining 75 percent of the vote, and campaign dropout Bob Dole from next door Kansas was winning 21 percent.

Dole's enduring regional popularity aside, Bush's relatively low vote total seemed further evidence of the difficulty he might face in farm states in the fall campaign. The vice president lost races in Iowa, South Dakota and Minnesota before routing the field to clinch the nomination.

Bush, who has locked up the GOP nomination and has no active opposition in the remaining primary states, looked forward to receiving President Reagan's endorsement tomorrow.

Dukakis, in contrast, was several hundred delegates ahead of Jackson but several hundred shy of the total needed to claim the Democratic nomination.

Aides expressed confidence he would command a nominating majority by the time the primary season ends on June 7 with elections in California, New Jersey and two other states, and Dukakis has begun campaigning with one eye on Jackson and the other on the fall campaign against Bush.

Addressing Quincy House seniors last night, Dukakis campaign manager Susan Estrich said her candidate will be campaigning hard in California and New Jersey and will be courting the remaining "superdelegates," in order to lock up a first ballot victory at the Democratic National Convention in Atlanta.

In response to a question on who the Massachusetts governor would choose to be his running mate, Estrich said "to talk about the vice presidency in any more detail would be premature... We will be spending most of our time working" to round up the necessary delegates.

ABC said its polling in West Virginia indicated that Dukakis was acceptable to voters across the political spectrum, although nearly 30 percent of the voters said they didn't know how to describe the Massachusetts governor's ideology.

ABC polling analyst Doug Muzzio said a majority of liberals and moderates and a plurality of conservatives said Dukakis' views were "just right" as opposed to too liberal or too conservative.