Maryon Allen, Sen. James Allen's 54-year-old widow, has accepted an interim appointment to his Senate seat and plan to seek election to the office in the fall campaign.

Gov. George C. Wallace, said to want the office himself, appointed Mrs. Allen yesterday and will call a special election to coincide with the general election on Nov. 7.

Wallce announced three weeks ago his withdrawal as a candidate for the seat to be vacated this year by Sen. John Sparkman (D-Ala.) when he retires. Wallace's press secretary reported, however, that the death of Sen. Allen "changed many things."

The governor wrote in last Sunday's Washington Post that his paralysis from an assassin's bullet in 1972 had contributed to a situation where "all of the circumstances involved were more than I could accept." But later in the week, press secretary Billy Joe Camp said letters and phone calls urging Wallace to run had caused him to reconsider.

Former state chief justice Howell Heflin and Rep. Walter Flowers (D-Ala.) are the strongest announced candidates for the full, six-year term of Sparkman's seat, and both have indicated they would remain in that race. There are two years left of Sen. Allen's term.

Mrs. Allen is now the only announced candidate for her husband's seat. A former journalist, she had been an active aide for her husband in his public life. Political observers say she would make a strong candidate, although Wallace's renewed interest indicates he seems to think he could take the seat from her.

Before it was known that Mrs. Allen wanted to run for the office, it had been widely reported in the state that she would be offered the interim appointment. Wallace went through with the plan even though he may decide to run against her.

Camp said Mrs. Allen and Wallace discussed the appointment for the first time Wednesday afternoon, the day after her husband's funeral. Wallace described her in a press conference in Montgomery as a "gracious lady and a strong person who, in my opinion, will serve Alabama well in the U.S. Senate."

"Maryon will carry on Jim's work on behalf of the people of our state and nation," he said.

Thirty minutes later, Mrs. Allen released her statement in Alabama and Washington accepting the appointment and saying she would "continue to espouse the great principles of government to which Sen. Allen dedicated his life."

"When I cast a vote on the floor of the U.S. Senate," she said, "it will reflect the philosophy he expressed so eloquently and so strongly during his almost 10 years of service."