The push to win Maryland for Walter F. Mondale, regarded as an uphill battle in a usually Democratic state, intensified today with an appeal by vice presidential candidate Geraldine A. Ferraro for support in the black community and the announcement that Mondale himself will campaign here on Wednesday.

Democrats in Maryland, a state once assumed to be a Mondale stronghold because it was one of just six states carried by President Carter in 1980, are hoping that the back-to-back visits by their standard-bearers will turn the tide that has been running in President Reagan's favor since September.

"This is the beginning of the final push of the last week for the Democrats," U.S. Sen. Paul S. Sarbanes said tonight at a fund-raiser for the Democratic ticket.

Recognizing that the key to a Democratic victory in Maryland lies with black voters in Baltimore and Prince George's County -- two areas carried by Jesse Jackson in the May 8 primary -- party strategists booked Ferraro in the heart of this city's minority community in West Baltimore today. She made precisely the kind of appeal they were looking for.

"Every American has a good reason to vote for Walter Mondale, but blacks, women and the disadvantaged have only themselves to blame if they stay home on Nov. 6," Ferraro told a group of several hundred enthusiastic black community organizers gathered at a church-run day-care center.

Flanked by a dozen 3- and 4-year-olds holding red, white and blue balloons in the Union Baptist Church community center, Ferraro criticized the Reagan administration for pushing "policies that have been a disaster for black Americans."

It was the kind of message that Democratic and Republican strategists alike say could make the difference in an overwhelmingly Democratic state that has defied the registration numbers by giving Reagan a consistently strong lead in the polls since September.

"This is a close campaign," Sarbanes said today. "We'll win if people don't sit home. Politics can't be a spectator sport."

Some blacks who listened to Ferraro today promised that they would not be spectators on election day, despite grumblings in the black community in recent months that the Mondale campaign has not reached out to Jackson's constituency.

"My minister would beat me up if I didn't vote," said Beatrice Riley, a Union Baptist Church member who yelled with excitement that she had shaken Ferraro's hand. "The reverend is very good about voting and getting us to the polls."

Today's appearance by Ferraro was the first of a flurry of campaign punches, including visits by former U.S. representatiave Shirley Chisholm and San Francisco Mayor Dianne Feinstein, that Maryland Democrats hope will wear down Reagan's persistent lead in the polls.

The ticket will receive an added boost this week when radio ads taped by U.S. Rep. Parren J. Mitchell -- the state's pre-eminent black politician -- are aired on Baltimore's major black radio station.

The ads ask black voters not to "turn their backs" on slain civil rights leaders Medgar Evers and Martin Luther King Jr. by sitting out the election.

Sarbanes and other top Democrats have steadfastly refused to credit a series of surveys that have shown Reagan with a lead of between nine and 13 points in Maryland since September.

Local Democrats, pointing to a surge of interest since the first presidential debate on Oct. 8, argue that the polls have not shown the depth of enthusiasm for the national ticket.

That kind of sentiment was echoed tonight at a Baltimore fund-raiser featuring Ferraro that drew about 1,500 Democrats and raised about $200,000 for the national ticket.

"You can like Ronald Reagan, just don't vote for him," Ferraro told the party faithful from a podium crowded with state and local officeholders.

Mondale is to campaign Wednesday at the Inner Harbor, the centerpiece and symbol of Baltimore's urban revival.

The Mondale-Ferraro campaign rejected appeals by a coalition of black ministers in Baltimore to bring his campaign to one of this city's black neighborhoods, rather than the glitzy shopping area overlooking the harbor.

Despite some talk within this city's black ministerial alliance of a possible boycott of the Inner Harbor event, a key black minister, state Del. Wendell Phillips, said today that the community would unite behind Mondale, and that the Democratic ticket would carry the state.