Emma Patton sat in a small room in an office building across from the U.S. Capitol yesterday and telephoned black elected officials around the country.

Across town, Vice President Mondale sat in his office calling Democratic senators.

Mondale and Mrs. Patton, a District of Columbia senior citizen who usually works in Del. Walter Fauntroy's campaign, were among countless people throughout the city lobbying a shrinking number of undecided senators to vote today for a constitutional amendment granting residents of Washington the right to elect senators and representatives.

The undecided senators found themselves under tremendous pressure yesterday from both supporters and opponents of the amendment.

On the Senate floor, Sen. Edward M. Kennedy (D-Mass.), the amendment's floor manager, was quietly chatting with colleagues while urging their support.

Fauntroy, the city's only congressional representative was meeting with other senators urging their continued support for the amendment or trying to sway fence-sitters.

"I'm cautiously optimistic," Fauntroy said near the end of the day. "There are still a few holdouts."

City Council Chairman Sterling Tucker, a candidate for mayor, had a talk with Sen. John H. Chafee (R-R.I.), who said he will vote for the bill.

Mayor Walter E. Washington, who made some telephone calls during the weekend in behalf of the bill, yesterday sent an open letter to all senators asking them "to remedy an unconscionable wrong" that has denied District of Columbia citizens full congressional representation.

Yesterday evening Mondale was to receive a complete list of undecided senators and a request from Fauntroy and Kennedy that he call the senators to persuade them to vote for the bill.

Meanwhile, block elected officials from City Council members to mayors in state from North Carolina to California found themselves receiving telephone calls from Mrs. Patton and five other women.

The women, working under the direction of Fauntroy's staff, called officials in those states where a senator or senators were still on the fence.

The request from the women was always the same - "your senator (the appropriate name) is key to the passage of this measure," so please wire or call him in Washington and ask for his support.

New Orleans Mayor Ernest Morial said he received one of those calls Friday asking him to contact Sen. F. Bennett Johnston (D-La.). Morial said he did so.

Fauntroy, to underscore his view that the amendment is the "civil rights act of 1978," has arranged for NAACP executive director Ben Hooks, Urban League executive director Vernon Jordan, Coretta Scott King and Martin Luther King Sr. to be present today and help with last-minute lobbying.

Self-Determination for D.C., a coalition of local and national organizations, activated its own nation-wide lobbying network to further bombard senators on the eve of the vote.

"We want to firm up the soft votes and to turn around the ones that are not implacable in a negative position," said executive director Elena Hess.