President Reagan's deadlocked Social Security advisory panel agreed yesterday to meet one more time next Friday after chairman Alan Greenspan told members the White House has hinted that it is ready for serious behind-the-scenes discussions on ways to save the system.

"We damned sure don't have a consensus" on how to find the $150 billion to $200 billion needed over the next seven years to ward off insolvency, ex-representative Joe D. Waggonner Jr. (D-La.) told reporters after the commission had spent two hours hashing over minor problems while failing to discuss major proposals for raising revenues or cutting costs.

The most important recommendation on which they did agree, on a divided vote, was to take Social Security out of the federal budget, of which it is now about a fifth, in order to depoliticize it.

Sen. William L. Armstrong (R-Colo.), a commission member, said he saw no point in further meetings unless the president and House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) could make contact in some way and block out at least general guidelines on what kinds of solutions both could accept.

Otherwise, he said, anything recommended would be knocked down immediately by one or the other.

Although Greenspan said nothing publicly about his discussions with the White House, he announced as the commission meeting ended that he believed there "is still some movement" possible and therefore it would be a good idea to meet again next Friday instead of giving up.

Members of the commission said this decision was based on private discussions in which Greenspan reportedly said the White House "had held out the possibility of behind-the-scenes negotiations."

During the comission's open session, Gray Panther leader Maggie Kuhn sought to address the commission from the audience in the Senate Finance Committee room where the meeting was being held, to protest possible benefit cuts and other reductions in programs for the aged. However, she was not recognized and was removed from the room by police.

Waggonner, discussing the White House position, said he was disturbed by the fact that some White House staffers, whom he declined to identify, "would like to make Social Security voluntary, I am reliably told."

Commission members have reached agreement on several issues, such as compulsory coverage for newly hired federal workers and employes of nonprofit organizations, removal of the trust funds from the federal budget so Congress will not be tempted to cut benefits in order to reduce the budget deficit each year, the need for stabilizing and fail-safe mechanisms to meet unexpected drains on the funds and the size of the deficit -- $150 billion to $200 billion annually over the next seven years, and 1.8 percent of taxable payroll over the next 75.

But the 15 members, five appointed by the Democratic leaders of Congress and the rest by GOP leaders and the president, are at an impasse over possible benefit cuts and revenue increases. The Democrats generally favor fewer cuts and more tax increases. The Republicans generally favor more cuts and fewer tax increases.

Yesterday, member Robert A. Beck, chairman of Prudential Insurance Co., circulated a plan to solve the deficit by cuts in the annual cost-of-living adjustment, raising the retirement age gradually to 68 and reducing the basic level of benefits for future retirees.

Democrats said this plan was unacceptable, as, they said, was a proposal by National Association of Manufacturers President Alexander Trowbridge which leaned somewhat less on benefit cuts and somewhat more on tax increases.

On the other hand, a plan by Democratic member Robert Ball, former commissioner of Social Security, which made up almost all the deficit by tax increases of one type or another, has received a cool reception from the Republicans.