A mass showing of top administration officials on Capitol Hill last night wrung slight concessions from two Maryland Democratic critics of President Reagan's drug-testing plan, but key disputes remained to be ironed out in another meeting today.

The administration announced guidelines earlier this year for conducting urinalyses of federal workers in sensitive positions.

Rep. Steny Hoyer moved to block the tests, and Sen. Barbara A. Mikulski fought for detailed procedural safeguards for federal workers that would result in considerable delays.

Mikulski said that she and Hoyer were "rethinking" whether to require the administration to reissue its guidelines as time-consuming regulations "in light of the comments" made at last night's meeting.

Hoyer said he had also agreed to eliminate the possibility that a single small agency might be allowed to hold up the government-wide program.

Earlier drafts of a compromise had stipulated that all government agencies be ready to implement drug tests before any could start.

Six top administration officials -- including Attorney General Edwin Meese III, Health and Human Services Secretary Otis R. Bowen, Office of Management and Budget Director James C. Miller III and Office of Personnel Management Director Constance J. Horner -- met yesterday for an hour with Hoyer, Mikulski, Sen. Dennis DeConcini (D-Ariz.) and Sen. Pete V. Domenici (R-N.M.) on the eve of a House-Senate conference on the fiscal 1987 supplemental appropriations bill, to which the drug language is attached.

Four drafts of drug-testing language have circulated between administration officials and Capitol Hill staffs, but the compromise process was interrupted Friday by an administration press release that accused Hoyer and Mikulski of trying to thwart the program through behind-the-scenes maneuvering.

"It is ironic that members of the Maryland delegation would attempt to thwart the government's drug-testing program so soon after a tragic train accident in their home state killed 16 innocent people in a case in which some train operators were shown to have used drugs," the press release said.

Hoyer said he thought one purpose of last night's highly unusual summit was to ease the administration's "embarrassment" over the press release. "Director Miller did not feel it made tactical sense" in the midst of negotiations, he said.

Meese opened the meeting and inadvertently handed Mikulski an opportunity to bring up the issue by asking her how she was, said James Abbott, Mikulski's press secretary.

"I'm not well, Mr. Meese," she responded, according to Abbott. "I'm not well at all after your press release."

Meese then moved to the

substance of the drug-testing language, Abbott said.

DeConcini said four points of disagreement remained: Whether all tests must be uniform. The administration guidelines give agencies wide latitude to determine whom to test and for what substances.

Which agencies would be exempt. All parties have agreed to exempt the Transportation Department and the Army. Considerable disagreement remains over whether to exempt the Navy and Air Force because their programs were not in effect when the president's drug-testing order was signed Sept. 15. How to expedite court challenges to the tests. The administration fears that court suits to stop testing might halt all drug testing. Hoyer said he was open to negotiation on the point. Whether to require that tests be implemented under regulations instead of guidelines. The administration contends that its guidelines are mandatory and that asking that they be put into regulation form is only a delaying tactic.

Mikulski said yesterday's meeting "clarified goals. We all agreed we want a drug-free workplace and we want to ensure reliability and accuracy in testing and the protection of employes' constitutional rights."

"I am basically opposed to random testing of public employes on grounds of constitutionality," Hoyer said.

"However, there is significant sentiment in the Senate on both sides of the aisle that we move ahead with a program for people in safety areas, especially transportation," he added.

"If this is going to happen I want as much due-process protection as possible."