Congress approved yesterday Washington's purchase of the four-acre Shapiro tract for development into a park, long-sought by residents of the Adams-Morgan neighborhood.

Mayor Walter E. Washington promptly sent his director of general services, Sam D. Starobin, to the tract's owners with a formal offer to buy the land at Adams Mill and Ontario roads NW for an appraised value of $1.6 million.

If the owners refuse, Washington told a District Building news conference, the city will file a condemnation suit that would assure immediate city acquisition and let a court set the final price.

Yesterday's actions were greeted with jubilation by City Council member David A. Clarke (D-Ward 1), who had been seeking the funds since 1975, and by community leaders who were invited to the mayor's news conference.

"In many ways, this park has come to represent the spirit of the Adams-Morgan community, the catalyst," said Frank Smith, chairman of the Adams-Morgan Organization.

Walter Pierce, who organized the Ontario Lakers Youth Program and mobilized neighborhood crews to erect temporary playground equipment on the vacant land, said he was on the verge of realizing a dream of 14 years.

By making yesteday's purchase offer to Maurice an J. B. Shapiro, city officials said they hope to head off a scheduled March 31 sale of the land to the Holladay Corp. That firm has announced plans to build 156 town houses on the site in price range from $65,000 to $100,000.

The mayor said two subcommittees of Congress acted speedily in the funds after he told them that impending private sale was jeopardizing plans for the park.

Techniclly, the city had asked both the Senate and House D. C. Appropriations subcommittees for permission to transfer $1 million previously ear-marked for other projects to purchase the Shapiro tract. The city has another $1 million for the Shapiro project available from other sources.

Sen. Patrick J. Leahy (D-Vt.) said his subcommittee approved the transfer on March 9. That was followed yesterday by a similar notification from Rep. William H. Natcher (D-Ky.). That represented final action.

Yesterday's action came precisely a year and a day after the city made its formal request for the fund transfer. The request was sidetracked when a dispute brroke out between Leahy and Natcher over the enactment of the city's formal 1978 budget. The dispute is still going on.

Natcher had opposed purchase of the tract when it was first proposed because he felt there was too great a dispartily between the price the city planned to pay and the land's assessed valuation for tax purpose.

Originally, Natcher said, the proposed price was $4 million, while the assessed valuation $351,000. The assessment went to $1.1 million. With legal and administrative expenses, the outlay will be around $2 million. At congressional hearings, a majority of community leaders vigorously supported the park plan. A vocal minority opposed it, with one calling it "a luxury item we taxpayers simply cannot afford."

Starobin, who as general services director is the city's construction chief, said plans for the development of the park have not been prepared. Funds for the development will be sought in future budgets.

Clarke, the neighborhood's City Council member, said the Shapiro tract is the only available open land in the area for a badly needed park and athletic playing fields. It once was the site of an apartment building.