President Carter endorsed Sue Ward for Congress last night in Baltimore, but her opponent Rep. Marforic S. Holt (R-Mid.). got help here Tuesday night from H. Earle Schaefer, which may be more important in determining the winner of the House seat in the 4th Congressional District of Maryland.

Because Schaefer, who is running for the State Senate in northern Anne Arundel County, is, like Ward, a Democrat, he did not quite go so far as to endorse Holt. But Holt's invitation to attend Schaefer's fund raiser here illustrates how Holt, one of the most conservative Republicans in Congress has managed to win three times in a district where registered Democrats outnumber Republicans 3 to 1.

Holt's position is so strong that not only does she get invited to Democratic events, but politically-savvy Democrats show up at Holt affairs.

Del. Pat Aiken, a Democrat seeking reelection to the legislature in a Republican district around Annapolis, worked the crowd at a Holt fund raiser in Bay Ridge recently, saying "if you want to get elected around here, you have to go after the same voters that Marjorie does."

Aiken, a liberal who is philosophicallt attuned to Ward's views, is supporting Ward, but confessed after appearing with her at a candidates' night in Severna Park that "it's difficult to go all-out (for her) in the 33rd (Legislative District)" because it might jeopardize Aiken's own chances for reelection. Holt mingled comfortably Tuesday at La Fountain Bleau, a Glen Burnie catering house, among a crowd that included Democratic Sen. Paul S. Sarbanes and the party's gubernatorial nominee, Harry R. Hughes.

"I need the votes of Democrats to get elected," Holt explained as she slipped a glass of beer at the $50-a-person reception.

Democrats interviewed at the Schaefer fund-raiser generally were at a loss to explain the Holt phenomenon, usually falling back on generalities such as "she's well liked," or "she's helped us a lot."

Holt and Ward are "180 degrees apart" on nearly every major issue, according to Ward, who quickly added that "I'm not the flaming liberal that Warner Fornos was," referring to the Democrat chewed up by Holt two years ago.

Ward is soft-pedaling her liberaslism having observed that "Warner won every debate" and got clobbered at the polls.

Yet the differences between Holt and Ward are dramatic: Holt favors funding another nuclear carrier, Ward does not; Holt opposes any gun control, Ward wants handguns registered; Holt supports the Kemp-Roth tax cut plan, Ward opposes it; Holt is against labor law reform and the humphrey-Hawkins jobs bill, Ward favors them; Ward would reduce marijuans offences from the status of felonies; Holt would not.

At a candidates forum earlier Tuesday night at the Clearview Elementary School in Clinton, Holt demonstrated her political acumen by potraying her opponent's moderate views as wishy-washy in comparision with her own rigid conservatism.

The issue was abortion, and Holt said fortrightly that she was opposed to it, period, even though she believed her constituents were equally divided on her issue.

In her response, Ward glided over her support for abortion funding and concentrared on Holt's refusal to support funds for subsidizes adoptions and child care that Ward believes will be needed if abortion funding is curtailed.

"But how do you stand on abortion?" interrupted Holt, who having already given the audience the view that her own stand was courageous and upcompromising, forced Ward to come down on the other side of that hot potato.

Holt's performance was an example of her ability to thwart Ward's effort to focus attention on Holt's voting record, which Ward believes should be the main issue of the campaign.

At a candidates' forum a week earlier, sponsored by the Maryland Nurses Association, Ward hoped to capitalize on a friendly audience by talking about Holt's zero ratings by a nurse group and a senior citizens group, and her vote to allow states to rescind ratifications of ERA.

Holt frustrated Ward again by distributing fact sheets to illustrate her support of seniors and women, and pointing out that she eventually voted to extend the time for ratification of ERA.

"It's an uphill fight," observed Ward after the meeting.