John B. Connally, whose income in the last 16 months exceeded $1 million, is apparently the most prosperous of a generally prosperous lot of Republican presidential candidates, according to financial disclosure reports filed yesterday.

All the contenders who filed yesterday-Connally, George Bush. Sen. Bob Dole (Kan.) and Sen. Howard Baker (Tenn.)-are in the top 1 or 2 percent of America's income levels and all except Dole have substantial corporate investments.

All four have benefited from honoraria from Corporations and interest groups, even as they were running for the presidency. In the cases of Dole and Baker, the honoraria helped boost their incomes substantially. Such payments are legal, though corporate campaign contributions are not.

President Carter and his two most likely Democratic challengers also are far more prosperous than the average American. Carter has assets that make him nearly a milionaire; Sen. Edward M. Kennedy (Mass.) is heir to a multi-million-dollar fortune and California Gov. Edmund G. Brown Jr. has an official salary of $49,100.

The reports were filed for the first time under the new Ethics in Government Act. More filings, including President Carter's, are expected in the next few weeks. Liberal extensions to the May 16 deadline for filing the reports are being granted this year because the process is new.

Rep. Philip Crane (III.), another GOP hopeful, did not file a disclosure from yesterday. But Crane perviously released income tax information showing total income for 1978 of $97,700.

Dole had a $96,777 income last year, including $11,578 in disability benefits from a World War II injury and $27,000 in speech honoraria. His wife, until recently a member of the Federal Trade Commission, also had an income of more than $60,000, although it was impossible to calculate the exact amount from the reports.

As expected, Connally appeared to be the wealthiest of those filing yesterday, both in income and in assests. According to his disclosure, his gross earnings from his partnership in the Houston law firm of Vinson and Elkins were $620,623. He received $265,000 more from the activities of the Connally Ranch in Texas.

Connally's checking account alone dollars in director and trustee fees from corporations including the Greyhound Corp., Continential Airlines, the Dr. Pepper Co. and the Falconbridge Nickel Mines Ltd. of Canada. He received honoraria from the National Grain and Feed Association ($4,000) the National Auto Dealers Association ($3,480) and the Southern Wholesalers Association ($3,500), among others.

Connally's largest assets included a $50,000 investment in Entex Inc., a Houston-based oil and natural gas drilling firm, and a $250,000 investment in the First City National Bank of Floresville, Tex.

Dole's only personal assets are a $15,000 to $50,000 savings account and his contributions to the Civil Service Retirement Fund. His wife, however, is a wealthy woman with large savings, stock and business holdings, and a sizable annual income. The minimum value of her holdings is $330,000, according to the reports.

The $27,000 Dole received in honoraria included $2,000 from the Food Marketing Institute, $1,500 from the National Association of Realtors, $1,500 from the Nation Corn Growers Association, $1,000 from the New England Mutual Life Insurance Co., $150 from the Brookings Institute and $350 from a political forum conducted by newspaper columnists Rowland Evans and Robert Novak.

More than one-third of Mrs. Dole's assets were held in a blind trust while she served as an FTC commissioner, and were invested in a series of bluechip stocks, including Sears Roebuck Co., E.I. duPont de Nemours Co. and Florida Powder and Light Co. She also owns rental property and a partnership in a charlotte, N.C., realty company.

Bush, who said he worked in 1978 as an author, lecturer and business consultant, listed consulting and director fees from two banks totaling $121,000 for 1978. He listed another $50,000 in honoraria for appearances and before schools, corporations and business organizations, and at least $52,000 worth of dividend and interest income.

Bush continued to earn large honoraria-some as high as $5,000-during the first months of this year, when he was running of president vitually full time.

Baker reported a Senate salary of $65,000 and honoraria in 1978. He reported that he donated $3,000 in additional honoraria to charity because of the limit.

Bush, a Houston-based businessman and former governmental official, reported assets-mostly in stocks and bonds-of at least $700,000 as of April 30. Bush listed income in 1978 of more than $250.000.

Baker, the Senate majority leader, who has not yet formally announced his candidacy but who seems sure to run, reported a net work of at least $460,000 in real estate, partnership interests and stocks and bonds. Baker's income in 1978 was at least $300,000, according to his report.