Rep. John B. Anderson, who failed to win a single primary as a Republican, has scheduled a news conference today to announce that he will run for president as an independent.

The move has been expected for more than a week. It will leave only two remaining contenders for the GOP nomination, front-runner Ronald Reagan and George Bush, who won an upset victory in Tuesday's Pennsylvania primary.

The Illinois congressman plans to run a media-oriented campaign directed by David Garth, a New York political consultant. It will be based on the assumption that large numbers of voters are disenchanted with the likely nominees of the two major parties, Jimmy Carter and Ronald Reagan, and will be willing to back an independent.

This is buttressed by several national polls showing Anderson currently has the support of about one-fifth of the electorate. A national Washington Post poll last week, for example, reported Anderson would get 17 percent of the vote in a three-way race with Carter and Reagan. Carter polled 42 percent of the vote in the matchup, Reagan 35.

Historically, independent and third-party candidates haven't fared well in American elections, and most political experts regard Anderson as more of a spoiler than a realistic winner in the general election.

But the Anderson candidacy has sent waves of uneasiness through both parties. This has been particularly acute in the Carter campaign because polls indicate Anderson's appeal is strongest among Democrats.

Robert S. Strauss, Carter's national campaign chairman, yesterday called Anderson's candidacy a "debilitating" exercise and suggested "it will cost us [the Democratic Party] state legislatures and candidates for the Senate."

"I think it hurts the process and that's important," Strauss told a news conference. "It distorts the systems. The two-party system has served us extremely well."

Former president Gerald R. Ford took a similar tack at a news conference in Chicago, calling Anderson's candidacy "a mistake in judgment." He said he was a "strong believer" in the two-party system that has "served this country well for over 200 years."

The Anderson candidacy faces various obstacles including money, the lack of a party organization and getting on the ballot.As an independent, he will not be eligible for the $29 million in federal funds that Republican and Democratic Party nominess receive. His name also doesn't appear automatically on the ballot and he has already missed filing deadlines in Ohio, Maryland, Kentucky, Maine, Texas and New Mexico, which together have 78 electoral votes. To win the presidency, a candidate must capture at least 270 electoral votes.

New Jersey supporters of Anderson yesterday became the first in the nation to place his name on the ballot as an independent candidate. On the next-to-last day that names could be filed for candidacy, they submitted more than 4,000 signatures. Only 800 are required.

In another move, the League of Women voters announced it will sponsor three presidential debates and a vice presidential one this fall. But Ruth J. Hinerfeld, chairwoman of the league's Education Fund, said no decision yet has been made on whether to invite Anderson to participate.