Republican national leaders today expressed rising fears that the 1980 decennial census and the resulting reapportionment of election districts across the nation could have disastrous effects on the party if major gains are not made at the statehouse level in the next two years.

Republicans control both houses of the legislatures of only five states, and could find themselves out of the picture when new political boundaries are drawn on the basis of new population figures, a national conference of Republican state chairmen was warned.

The national Republican Party, which traditionally has concentrated its money and effort on the top of the ticket - presidential and gubernatorial races - has shifted its emphasis recently to a grass-roots rebuilding of the party, primarily because of the poor post-Watergate showing in the last congressional elections.

The statehouse-level election drive should now be accelerated if for no other reason than the the new census, several party officials warned the state chairmen and Republican national committee members.

Democrats control 5,128 seats in state legislatures, compared to the Republicans' 2,370.

"This is where it is all at. If we don't get control of some of these legislatures in 1980 in time for reapportionment, we're in big trouble," said Paul Priolo, vice president of the Republican National Legislative Association and the minority leader of the California Assembly.

Steven Stockmeyer, director of the National Republican Congressional Committee, said, "We have a very bad situation the way the [apportionment] lines are drawn now. What we want to make sure is that the condition doesn't get worse after 1980."

Stockmeyer said that Democrats can increase their seats in the U.S. House of Representatives by raising their popular vote total by only 1 per cent, while Republicans would have doesn't get worse after 1980."

congressional year to take control of the House.

The national party should funnel more money and manpower into the state races to minimize the losses of safe Republican seats as a result of reapportionment, Stockmeyer urged. Also, he said, the party shoul begin now to undertake population analyses and assess voter trends so that if Republicans are in a position of bargaining strength when reapportionment comes up, they will be prepared.

"There's nothing more embarrassing than to go to a legislative session or to a court unprepared to make the best case," he told the state chairmen.

Murray Dickman, director of computer services for the Republican National Committee, said last year the GOP won 44 per cent of the congressional vote cast for the two major political parties but holds only 33 percent of the seats.

In California, he said, Republicans won 44 per cent of the vote but hold only 29 per cent of the seats in the legislature.

"There is no such thing as nonpartisan redistricting. It's a myth and you ougth to know what effect the census will have," he said.

Republican National Chairman Bill Brock, in remarks prepared for delivery Friday, urged the party to appeal to the middle-class American dream - "te dream of home ownership, the dreams of better schools, lower taxes, health care at a reasonable cost, personal security and jobs."

These aspirations have become dreams im the literal sense as the average price of houses has climbed beyond the reach of all about one in four Americans, and the cost of a college education has reached $20,000, Brock said in a message that appeared to shape the domestic issues theme of the 1978 elections.

He attacked what he termed President Carter's retreat from a campaign promise never to raise taxes of lower and middle-income groups - Congressional Budget Office figures indicate that adminstration budget proposals will raise taxes $130 billion to $339 billion by 1982, he said.

"Let the Democrats continue to heed the demands of the super elite or the special interest militans. We will listen to the dreams of the family, the dreams of a decent job, a healthy family, a secure environment . . . a dream of a better quality of life." Brock said.

As the state chairmen's conference wound down, the National committee readied itself for what promises to be spirited debate Friday on the Panama Canal treaties.

At least one resolution opposing the treaties has already been drafted and in informal conversations, most leaders appeared to have some objections to the pact, if for varying reasons.

One of them, Bernard M. Kilbourn, New York state chairman, said, "I don't think it will be a cause celebre. The question isn't whether you give the cow away, it's whether you pay to give the cow away," a reference to payments to the Panamanian government for operation of the canal.

Kilbourn said recent surveys had shown that 650 state committeemen and county leaders who responded in New York were 2-to-1 against the treaties, and that a "consensus" of New York congressmen opposed it.