The Prince George's County Council voted unanimously yesterday to recommend that water and sewer rate increases proposed last October by the Washington Suburban Sanitary Commission be delayed until July.

All three of the county's representatives on the WSSC -- which serves Prince George's and Montgomery counties -- say they will support the council's action.

The WSSC's proposed rate rise will add approximately $20 a year to the average consumers's combined water and sewer bill.

"The [WSSC] members from the county have to work together with the council on this kind of thing," said Johanna Norris, one of Prince George's three commission members. "All three of us have agreed to hold off on any rate changes until July."

Last fall the WSSC recommended the rate increase because customers -- plagued by a wet, soggy summer -- had not used enough water.

The proposed increase, which would raise customers' water bills by 6 percent and sewer bills by 18 percent, were met with protest from both county councils and consumers who complained of having to pay for the summer's heavy rains.

WSSC general manager Robert S. McGarry told the Prince George's council yesterday that unless water and sewer increases were implemented before July, the commission could face a $6 million cash flow shortage by the end of fiscal 1980.

Without the rate rise, he said, the WSSC would most likely be forced to internally finance a cash flow shortage from March through June.

"It won't hunt us too badly," McGarry said, "but it will certainly have an effect on our bond rating. You know that's exactly how New York and Cleveland got into so much trouble."

The three WSSC members from Montgomery County are in favor of the rate increase, which must be approved by a majority of the six commission members. The delegation now is deadlocked 3 to 3, as a result of yesterday's vote.

"I don't think there is any doubt the commissioners from this county will wait until summer before supporting water or sewer rate modifications," said Lawrence Brooks, a member of the Prince George's WSSC delegation.

WSSC's general manager, Robert S. McGarry, surprised the county council yesterday by recommending that the longer the increase is delayed, the higher it will be.McGarry said that to balance the WSSC's budget, they would ask for a 21 percent increase in water rates and a 35 percent increase in sewer rates in April.

"It's really a question of whether you want to authorize the increases for April or whether you want to wait until June and raise water and sewer rates, by 27 percent and 45 percent," McGarry said.

Council Administrator Samuel E. Wynkoop presented a report showing that budget cuts have by the WSSC and an increase in water and sewer usage by customers left the WSSC with a $1.4 million surplus at the end of fiscal 1980.

"The budget cuts already seem to have had a substantial impact and the WSSC's estimates on water use seem a bit conservative," Wynkoop told the council.

In November, the WSSC initiated a freeze on hiring, deferred $2 million worth of construction work and cut equipment purchases by $800,000.