Anthony J. Cicoria, the Prince George's County Council member convicted Tuesday of stealing campaign money and lying on his tax returns, decided yesterday to pull out of his reelection campaign and join the county Democratic leadership in supporting last-minute write-in candidate Stephen J. Del Giudice.

Party leaders have scrambled to boost Del Giudice's candidacy to avoid a potentially embarrassing outcome in the council race. Without Del Giudice, voters would be left with the choice of a convicted incumbent or his Republican challenger, a two-time candidate who briefly spent time in a state mental institution in the early 1970s after he threatened his opponent with a "poke in the nose."

The new development in the council contest is the latest in a topsy-turvy political season in Maryland. Del Giudice is one of handful of Maryland politicians to launch write-in candidacies after being defeated in the primary. Others are Montgomery County Executive Sidney Kramer and former Prince George's County state senator Tommie Broadwater.

Cicoria said he arrived at his decision to withdraw without consulting his council colleagues or the county's top Democrats.

His announcement came after a late Thursday night meeting at which party leaders agreed to back Del Giudice, the three-term mayor of Takoma Park and president of the Metropolitan Washington Council of Governments.

Athough it is too late for Cicoria to take his name off Tuesday's ballot, he said he would vote for Del Giudice and is urging his supporters to do the same in the race to represent the 2nd Council District, which includes Takoma Park, University Park, Mount Rainier and Hyattsville.

Del Giudice "is a fine, quality individual who would do an outstanding job, would make the people in the 2nd District proud," Cicoria said. "Steve will continue not only the fine constituent service, he will also be a model for all elected officials in Prince George's County."

The Republican on the ballot is J. Lee Ball Jr., who has been disavowed by his party.

In a "Dear Friends" letter written hastily yesterday, Cicoria said his "personal and legal concerns require all my immediate attention." Cicoria, who has served on the council since 1982, is scheduled to be sentenced Dec. 18. At that time, he would be suspended from office pending any appeal of his felony conviction.

If Cicoria is reelected despite his conviction, his suspension from office shortly afterward could create a chaotic situation. It is unclear whether Cicoria's seat would remain vacant during his appeal or be filled temporarily by the council or through a special election.

Democratic leaders said the chaos could be avoided with the election of Del Giudice. They described Ball, 59, who works in a College Park car dealership, as unqualified for office. "The Republicans should have had a credible candidate," said County Executive Parris N. Glendening.

Ball ran against Glendening in 1982 and against County Executive Winfield Kelly before that. A former Democrat, he said he spent 12 days under observation in a state mental hospital in 1972 after he threatened then-Rep. Lawrence J. Hogan (R-Md.) with a "poke in the nose."

Talk of a write-in candidacy, considered exceptionally difficult so late in the campaign, began soon after Cicoria's conviction. Del Giudice, who finished second to Cicoria in a four-way Demoratic primary, was the immediate favorite.

The concerns of party leaders intensified Thursday when the Baltimore Sun endorsed Ball. Yesterday, the Sun withdrew its endorsement of Ball and urged voters to write in Del Giudice.

Thursday night, party leaders convened by Rep. Steny H. Hoyer (D-Md.) met for two hours to discuss the Del Giudice campaign. Out of that meeting came a pledge by Democratic politicians to plow $15,000 into the effort, which is to include two mailings to the district's 27,000 voters. Democrats also plan to have campaign workers near each polling place in the district to explain how to write in a candidate.

A news conference and rally for Del Giudice are scheduled this afternoon at Hyattsville City Hall, with Glendening, Hoyer and others expected to attend. Glendening estimated that between 2,500 and 3,000 votes could win the election. In both party primaries Sept. 11, 7,876 voters cast ballots for the candidates in the council race.