NEW ORLEANS, JUNE 27 -- Thirteen months before they return here for their national convention, Republican Party leaders are counting on "the kiddy pool" factor to keep them in control of the White House. They rate their chances high in 1988 largely because they think voters will prefer the experienced national figure they expect to nominate over any of the Democrats' youthful and little-known contenders.

Despite concerns about the after-effects of the Iran-contra investigation on President Reagan's reputation and their top pollster's report of growing public negativism on the economy, GOP officials in the 10 biggest states expressed confidence their electoral votes will stay in the Republican column.

Their key assumption is that the baby-boom voters they hope will swell the turnout next year prefer an experienced, older candidate echoing Reagan's antitax, antispending rhetoric to a younger Democrat espousing activist government.

Frank B. Holman, the New Jersey state chairman, called the younger generation "the hope of the Republican Party. That's where we can eat them up. Those young people are very ambitious. They want it all and they want it now, and they don't want to see it taxed away. They don't care if Aunt Tilly is being taken care of in the nursing home or not; Aunt Tilly better take care of herself."

His emphasis on the economic opportunity message was echoed by most of the others at a round table of top GOP officials from the 10 largest states, arranged by The Washington Post during the meeting of the Republican National Committee that concluded today.

Almost without exception, these officials believe their party will nominate either Vice President Bush or Senate Minority Leader Robert J. Dole (R-Kan.), men in their 60s with long years of federal experience. Unless both stumble, which the state chairmen concede is possible, these Republicans are quite content to run their "old hands" against any Democrat drawn from what RNC cochairman Maureen Reagan derisively called "the kiddy pool."

"We have the known quantities," said Edward Lourie, executive director of the New York GOP. "In the long run it may help the Democrats" to showcase a large number of young aspirants who can run again, "but in 1988, they'll be hurt by the Jimmy Carter factor -- the fear of the unknown -- and the Jesse Jackson factor -- the fear of the one Democrat who is well-known."

The electoral success of such low-key governors as New Jersey's Thomas H. Kean and California's George Deukmejian has convinced the state chairmen that "demonstrated competency" will be more valuable next year than "new ideas."

"You see these managerial Republicans emerging as the people the voters trust," said Pennsylvania chairman Earl M. Baker. "You don't have to be flamboyant," said California chairman Bob Naylor, "but you do have to know where you're going."

"A new vision, but not a new person," agreed Ohio chairman Michael F. Colley. "Carter ended the fascination with novelty."

"We can win on the Reagan record," said Illinois chairman Don W. Adams, "as long as our candidate is known and respected. We're very comfortable with Bush or Dole."

Bush is viewed as the front-runner in almost all the biggest states and has close family ties to three of them: Texas, which is his adopted home, and Florida and New York, where his sons are party leaders.

In California, Bush has signed up so many of the early Reagan supporters that former senator Paul Laxalt of Nevada, a Reagan ally and intimate of much longer standing, has an opening only "if Bush falters," Naylor said.

The consensus was that Dole, with his appeal to business and farm leaders and his aggressive wooing of conservative former critics, has made himself the alternative to Bush in most of the big states.

Texas chairman George Strake said that even though Bush already has "about 90 percent of the national delegates in his hip pocket," he wasn't yet ready to write off the chances of Rep. Jack Kemp (R-N.Y.). "I told Jack recently that I see your rocket on the launch pad," Strake said, "but I don't yet see it taking off."

Kemp's current prospects in New York were described skeptically by Lourie, who noted that 35 county chairmen are already in the Bush camp. The other GOP contenders, Laxalt, former secretary of state Alexander M. Haig Jr., former Delaware governor Pierre S. (Pete) du Pont IV, and television evangelist Marion G. (Pat) Robertson, were viewed as long shots, although Robertson's ability to enlist new people in the GOP was noted with near-awe by Strake, Adams, Florida chairman Jeanie Austin and Michigan chairman E. Spencer Abraham.

Strake said he believed the party must welcome the new adherents "if we're ever going to be a majority," but Austin said their sudden appearance is overwhelming and alarming some "old-time party regulars. They wonder where they were when we were trying to build the party and why they are coming in now telling us how to do our business."

In the last five elections, Republicans have won three of the 10 biggest states, California, Illinois and New Jersey, each time; four others, Florida, Michigan, North Carolina and Ohio, four times; and the last three, New York, Pennsylvania and Texas, three times. Together, those states control 241 of the 270 electoral votes needed.

The strongest optimism about 1988 was expressed in the states where both the population and Republican voting bases have been expanding: New Jersey, North Carolina, Florida, Texas and California. All five now have Republican governors, and the GOP has been making inroads on Democratic strength at the local level.

More guarded were the leaders from New York, Pennsylvania, Ohio and Michigan, where Democrats won the key gubernatorial battles last year, and in Illinois, where, Adams warned, lingering farm problems may damage GOP chances of offsetting the traditionally heavy Democratic vote in Chicago.

Presidential pollster Richard Wirthlin, in an appearance before the national committee, said that despite the near-record period of sustained economic growth and the drop in unemployment, "declining numbers of Americans say they are better off than they were the year before." Wirthlin blamed the phenomenon on news media attention to problem areas like Louisiana, but warned, "Perceptions are as important as realities, so we have to drive home our message."

He also said that the Iran-contra affair and Democratic exploitation of the Social Security issue have damaged both Reagan and the Republican Party severely among women and the elderly. "Unfortunately, there is still a gender gap," he said, adding that identification with the GOP among over-65 voters dropped from 45 percent in early 1986 to 31 percent this year.

Despite the damage, Wirthlin said, Republicans go into the 1988 campaign only 10 points behind the Democrats in basic party strength compared to a 25-point gap eight years ago. Republicans are preferred over Democrats on several issues voters say are important, including world peace, combating drugs and appointing tough judges. The Iran affair ranked only 10th on a list of voters' concerns.

In a comment several of the state chairmen said is borne out by polls in their states, Wirthlin argued that Reagan is on strong ground in drawing the line with congressional Democrats on tax-and-spending issues in the fiscal 1988 budget. He said his surveys show that twice as many voters blame Congress as blame the president for the deficit; seven of 10 believe that the Gramm-Rudman-Hollings deficit-reduction targets abandoned in the Democratic budget resolution are extremely or very important; and almost nine of 10 would cut government services before they raised taxes.

"I didn't think we could run on the tax-cut issue again in 1988," California's Naylor said, "but taxes will be an issue if the Democrats make it one."

Repeatedly, the big-state chairmen expressed the view that the key contribution their presidential nominee can make to local victories in 1988 is presenting issues and a personal appeal that will swell voter turnout by attracting baby-boomers.