Mayor Walter E. Washington vetoed yesterday an emergency measure designed to authorize 2 to 10 per cent rent increases throughout the city, raising new uncertainties about the District's controversial rent control system.

After a day marked by political charges and legal maneuvering, the mayor and the City Council appeared to have reached agreement on a plan to extend the city's present rent control program for 90 days without permitting any immediate, across-the-board rent increases. Without emergency legislation, the city's 3-year-old rent control law would have expired next Monday.

After a series of turnabouts by the District government this month, it remained unclear yesterday how quickly the Council would act to provide for possible future rent rises.

The Council may seek to defer such rent increases until next spring or later by authorizing them as part of a long-term rent control bill, which is already under consideration. On the other hand, Council members indicated yesterday they may try to institute across-the-board rent increases soon by passing anohter form of emergency legislation.

Councilman Douglas E. Moore (D-at large), one of the mayor's chief supporters in the Council, hailed his veto yesterday as a political "coup" that had caught the mayor's Council critics off guard.

The mayor, by blocking the proposed rent increases, managed to separate himself from two prospective, although unannounced, candidates for his job - Council Chairman Sterling Tucker and Councilman Marion Barry (D-at large), both of whom had previously voted for the rent increases. The mayor has yet to announce whether he will seek re-election next year.

Tucker later charged that the mayor appeared to be "coming down on either side of the (rent control) issue" and that the mayor's veto might have had the effect of wiping out all controls on rents - an assertion disputed by the mayor - if the Council had not taken emergency action yesterday. "I don't see how that's a political coup," Tucker added.

Barry acknowledged that he himself had shifted ground since last week's Council vote to allow rent increases and he blamed the Council for acting with "sloppiness" and "haste." But he sought to belittle Moore's claim that the mayor scored a political coup on the rent control issue. "Even if he did," Barry said, "it wouldn't help him."

The mayor's veto yesterday followed several shifts by the Council, which has been grappling with the rent control controversy for months. Two weeks ago, the Council approved an emergency bill designed to extend existing rent controls for 90 days without allowing across-the-board rent increases. Last week, in a surprise move, the Council voted 7 to 6, to revise its earlier measure to permit rent rises, ranging from 2 to 10 per cent this winter.

Mayor Washington vetoed the second measure, contending in part, that it failed to provide adequate safeguards for tenants. At the same time, he said he would permit the earlier emergency bill - the measure that was designed to continue rent controls without providing for rent increases - to take effect without his signature, unless the Council passed some other "appropriate" legislation before next Monday night.

The mayor's dual actions caused some confusion and set off a sharp debate in the Council. Councilman David A. Clarke (D-one), an advocate of rent controls and opponent of the rent increases, charged that the mayor's actions relied on dubious legal arguments and he warned that the city's rent control system might lapse unless the Council passed another emergency bill. Because the Council had reconsidered and sought to withdraw its first emergency measure Clarke argued, the legislation might be later held by a court to be invalid.

The Council, after prolonged and sometimes pointed debate, then re-enacted the same emergency bill it had approved two weeks ago and sent it to the mayor. It provides for a 90-day extention of rent controls and no across-the-board rent rises. Aides to the mayor said he will almost certainly sign it, though they added that the legislation must be reviewed to make certain it contains no flaws.

At a news conference yesterday and in his veto message to the Council, Mayor Washington described his views on the city's rent control system in greater detail than he has offered in recent months.

At the news session, he said flatly that he believes rent controls "should be continued." He said that some across-the-board increase in rents appears warranted soon, though he declined to express a view on how steep the increases should be or when they should take effect. He said he would favor ending rent ceilings on highpriced luxury apartments at some point - perhaps as part of the longterm rent control legislation now under study by the Council.

In his veto message, the mayor objected to the Council's emergency rent increase measure because, he said, the bill omitted essential safeguards for tenants. Among these, he said, was a failure by the Council to require that buildings be in substantial compliance with the city housing code before rents may be increased. He also argued that financially pressed tenants need more time than the 30 days' notice provided in the Council's bill before their rents go up. He told reporters that 60 or 90 days' notice appeared more reasonable.