The D.C. Department of Human Resources has given Washington Medical Centre, Inc., an additional 60 days to complete its long-delayed and sometimes controversial plans for a new Doctors Hospital in downtown Washington.

The conditional extension to Aug. 11 was announced yesterday by Albert P. Russo, acting director of DHR. It was the third time that the hospital's planners have been granted more time on a certificate of need issued by DHR in 1973 for one year.

Russo acknowledged yesterday that the length of the extensions was unprecedented.

One of the major conditions on which the extension was approved is that the replacement for the 39-year-old hospital - currently located at 1815 I St. NW and scheduled for demolition in 1980 - be able to meet the medical needs of another group that also wanted to build a new medical facility downtown.

Group Health Association, Inc., the largest health maintenance organization in the area, had sought a certificate need to build a 184-bed hospital downtown. Yesterday Russo said that GHA's request has been denied.

The new plan submitted by WMC calls for locating the new Doctors Hospital in the Metropolitan Hotel at 1143 New Hampshire Ave. NW, which is also owned by WMC.

The renovated Metropolitan Hotel will contain only 265 beds instead of the 321 anticipated when WMC was planning on building a new structure. Russo said that by renovating instead of building, WMC will be able to hold down costs and open a new facility sooner. The result would be lower costs to patients, he said.

WMC's dealings with DHR over the certificate of need - a permit needed by the hospital in order to begin construction - came to public attention last fall in The Washington Post during a series of articles on former DHR director Joseph P. Yeldell and parking lots magnate Dominic F. Antonelli Jr.

Antonelli, until recently an officer of the hospital, negotiated with Yeldell to receive two extensions to the original certificate of need. One of those extensions allowed the hospital to transfer temporarily the probably site of the new building to land owned by Antonelli.

During the time of the negotiations, Yeldell received assistance from Antonelli in obtaining two personal loans totaling $54,000.

Yedell has said that the loans did not influence his decision on the hospital or other actions he took that apparently benefited Antonelli financially. These include orging the city to sign a $5.6 million, 20-year lease on a vacant building in Northeast Washington that Antonelli had purchase months earlier for $800,000.Antonelli has refused comment.

Russo stressed yesterday that the decision to extend the need certificate was his own.He had not discussed it with Antonelli, he said, or with Yeldell, who in early April was transferred from the DHR directorship to general assistant to Mayor Walter E. Washington.

Russo did not rule out another possible extension if the Aug. 11 deadline could not be met. "We'll cross that bridge when we get to it," he said.

In order to obtain the extension, WMC must give DHR full proof that it owns the hotel; submit plans for the renovation of the hotel and management of the new facility, provide documentation of satisfactory financing to complete the project and give proof that there has been substantial progress toward an agreement with GHA.

Russo said he expects the conditions to be met by Aug. 11, based on preliminary discussions with GHA and WMC officials.