Not only does it look as if New York Republican gubernatorial nominee Pierre Rinfret will be defeated by Gov. Mario M. Cuomo (D), he may also be defeated by Conservative Party challenger Herbert London in Tuesday's election.

Cuomo was the choice of 61 percent of likely voters surveyed by the Marist College Institute. Rinfret and London each had 11 percent. Right to Life Party candidate Louis Wein trailed at 2 percent and 15 percent were undecided.

Should London finish second to Cuomo, the Conservative Party would take over the No. 2 ballot spot for all national, state and local elections in New York for at least the next four years.

In Connecticut, Democrats could lose their status as a major party in state politics. State law stipulates that to qualify for state financing for primary elections a party must get at least 20 percent of the vote in each gubernatorial election.

Polls have consistently shown the Democratic gubernatorial nominee, Rep. Bruce A. Morrison, with less than 20 percent support. A poll last week had him at 12 percent. The Republican, Rep. John G. Rowland, has been drawing 25 to 30 percent. Former senator Lowell P. Weicker Jr. (R), who created the Connecticut Party for his independent bid for governor, has attracted about 35 percent support.

State Democratic Chairman John F. Droney Jr. said the 20 percent law "should be a wake-up call to Democrats who have been toying with . . . voting for one of the two Republicans."

If Weicker wins, the Connecticut Party will be listed at the top of the ballot in 1994.