Rep. Gladys Noon Spellman, the Prince George's County Democrat hospitalized in a semicomatose state since suffering cardiac arrest Friday, won an overwhelming victory yesterday over her little-known Republican challenger, Kevin Igoe, in Maryland's 5th Congressional District.

Spellman swamped Igoe, a 30-year-old former federal worker who entered politics with this race, by receiving 81 percent of the vote. She got 103,140 votes to Igoe's 24,728.

At a Democratic Party victory celebration last night at the Sheraton-Lanham Hotel, Spellman's press aide, Art Jaeger, said the vote was a "tribute to Spellman. It was a nothing race, it was rainy and ordinarily a lot of people might not have gone out, but anyone who had thoughts along those lines made a special effort to go out" as a demonstration of support for the critically ill representative.

Since her first race for Congress in 1974, Spellman, 62, has racked up increasing margins of victory over her Democratic and Republican opponents, earning a reputation for political invincibility. The election this year handed Spellman her greatest victory and provided one of the largest winning margins of any congressional race in the state.

From the beginning, Igoe's challenge posed little threat; his criticisms of her record as "too liberal" and his support for the Kemp-Roth tax-cut proposals drew little attention. Both numbers and time were on Spellman's side. Prince George's has a 3-to-1 Democratic registration and Spellman has spent many years attending to the needs of county residents, in particular the large bloc of federal workers.As a result, Igoe, was unable to break her grip on their loyalties.

Faced with the weak Igoe challenge, Spellman did not conduct a vigorous campaign and the county's Democratic Party virtually ignored the race until just four days before the election when Spellman was struck down by a life-threatening heart attack.

Spellman was rushed to the hospital Friday evening from a Laurel shopping center where she had gone to judge a children's Halloween costume contest and the campaign was thrown into turmoil. Concerned Democrats wondered whether Spellman would live through the election and quietly planned what they should do if she didn't.

Igoe immediately announced that he had canceled further campaign appearances out of respect for his opponent.

As Spellman, who has proved her political resilience over 18 years in elective office, struggled for her life in the coronary-care unit of the Greater Laurel-Beltsville Hospital, Democratic Party leaders began assessing the impact of her illness on election results.

Initially they were worried that reports of Spellman's critical condition might discourage many of her supporters from casting ballots in the congressional race, thus thwarting her reelection effort. They also feared that Republicans who had supported her in the past might now, with Spellman's future so clouded, desert her for their traditional GOP slate.

By yesterday afternoon it was clear that neither of those scenarios had developed and many voters, including Republicans who said they had never voted for Spellman in the past, apparently cast ballots as a sign of support for her struggle. The "sympathy factor," as one Democrat called it, may have been the most important factor in giving Spellman her largest victory.

With her long-expected victory in hand, the question that remains is whether Spellman -- the former PTA activist, county commissioner and county council member -- will be able to serve her fourth term. Although Spellman's heart has been functioning normally since her collapse, grave concerns remain about the condition of her brain.

If Spellman is unable to return to Congress, for whatever reason, the county political scene would become tumultuous. Spellman is the county's top elected Democrat and has made the 5th Congressional seat a "safe" one for the Democrats. Her departure would force the county to hold special primary and general elections in the next few months, which would provoke a scramble for her post and her power.

Spellman's lock on the 5th Congressional seat is seen by many observers as duplicated in the adjoining 4th Congressional District where four-term Rep. Marjorie Holt breezed by Democratic challenger James Riley with 72 percent of the vote. She got 116,162 votes to Riley's 45,869.

Riley, a history teacher, was unable to make serious inroads into Holt's support, despite his appearance on the Democratic Party line in a heavily Democratic district that includes southern Prince George's and Anne Arundel counties.

Like Spellman, Holt has been able to make her seat a "safe" one for her party by catering to federal worker constituents and casting conservative votes, especially on defense issues.