The District government's bid to strike a series of congressionally imposed mandates from next year's budget suffered what might be the final setback yesterday, when a joint House-Senate conference committee endorsed a bill that maintains all of the so-called social riders.

Bans prohibiting the District from legalizing marijuana for medical purposes or spending money on a needle-exchange program for drug addicts are now in both the House and Senate bills, as is language that would allow two cellular phone towers to be built in Rock Creek Park without additional local review.

Mayor Anthony A. Williams (D) and other District officials had asked the conference members to eliminate the riders, several of which had been in only one of the two versions of the bill. But on every matter brought up for debate yesterday, the riders were endorsed by the Republican-dominated conference committee.

The joint bill now goes back to the House and Senate for a final vote--perhaps before the end of this weekend--then to President Clinton for his signature or veto.

"It stinks," said Rep. James P. Moran Jr. (D-Va), who tried yesterday to eliminate several of the riders. "All we are talking about is letting the District of Columbia operate like any other city in the country does."

Ultimately, the conference committee agreed to a budget plan that appropriates $429 million in federal funds for the city, mostly for programs such as the corrections system and courts. The total District budget--including capital spending, enterprise funds and its $4.7 billion general fund--would be $6.8 billion.

The bill included tens of millions of dollars in extra money for a variety of city programs, such as expanded drug treatment and a $5 million cleanup of the Anacostia River. For that reason, Democrats were split late yesterday on whether they would urge Clinton to veto the District's budget bill for fiscal 2000.

Del. Eleanor Holmes Norton (D-D.C.) said the riders are so offensive that Clinton should follow through on a veto threat his staff made again yesterday. But Moran, the ranking House Democrat on the District budget panel, said, "It is a tough call."

Sen. Richard J. Durbin (D-Ill.) asked the conference members yesterday to compromise by just banning the expenditure of federal funds on a District needle-exchange program, while allowing the city to spend its own money for the AIDS-prevention effort.

But Sen. Kay Bailey Hutchison (R-Tex.) said the exchange might increase drug use without doing much to slow the spread of the virus that causes AIDS, an argument that prevailed. Republicans also noted that a nonprofit city agency already operates a needle-exchange program with private funds.

The bill endorsed yesterday also bans city spending on abortions or on health benefits for domestic partners. The conference committee adopted House language that would allow the city to count votes on the 1998 initiative on legalizing marijuana to treat certain medical conditions. But as approved by the House, the joint bill now would prevent the initiative from becoming law, even if voters approved it.

The joint Senate-House bill, if passed into law, would also allow Bell Atlantic Mobile to begin building two cellular phone towers in Rock Creek Park within a week after the budget goes into effect in October. The National Capital Planning Commission has not given final approval for the towers, which Bell Atlantic says are necessary to prevent "dead zones" in cellular service in the park, but the budget bill instructs the National Park Service to issue the permits anyway.

Rep. Ernest J. Istook Jr. (Okla.) asked his Republican colleagues to cut a provision banning the city from spending money on a lawsuit seeking voting rights for the District in Congress. Despite support from Democrats on the request, Istook's motion failed.

In several cases, the conference committee cut requests by the House for extra money for special initiatives, such as providing drug treatment for addicts who are on parole, probation or awaiting trail. That program would now get $7 million, instead of $13 million. But few of the special programs were eliminated entirely.

Extra funds adopted by the conference committee include:

* $5 million--instead of $8.5 million--to accelerate the placement of foster care children into adoptive homes.

* $18 million--instead of $20 million--to allow the city to reduce its payroll by offering severance packages to city employees.

* $5 million--instead of $7.5 million--for design work to expand the 14th Street bridge by one lane in each direction.

* $5 million--as proposed by the Senate--to allow the city to offer tax credits to property owners who renovate stores or businesses in rundown neighborhoods of the city.

* $1 million--as proposed by the Senate--for the police department to crack down on open-air drug markets.