The nation's governors, suspending talk of trade and tax revision, plunged into a partisan spat today over a GOP fund-raising letter that some Republicans called "innocuous" but Democrats branded "claptrap" laced with "lies."

The letter, mailed June 27 over President Reagan's signature, sought contributions to the Republican Governors' Association for 1986 statehouse campaigns, saying that Democratic governors "had teamed up with liberal Democratic leaders to block our plans aimed at balancing the federal budget."

After more than three hours of closed-door negotiations that overshadowed a speech on global competition by the president of Hewlett-Packard Co. and scuttled a scheduled debate on taxes, the Republican governors proclaimed that they meant no undue harm.

The apology averted a threat by the Democrats -- two-thirds of the National Governors' Association's membership -- to end the session's third and final day early or refuse to vote for Tennessee Gov. Lamar Alexander (R) as chairman, a post he was due as vice chairman.

"The language . . . was not intended to unfairly -- and I repeat unfairly -- characterize the position or record of any specific Democratic governor," said Pennsylvania Gov. Richard L. Thornburgh (R), chairman of the Republican Governors' Association.

"Future fund-raising letters on behalf of the Republican Governors' Association will be framed in terms consistent with this conviction and with that intention and will avoid any such characterizations," Thornburgh said.

The Democrats announced their acceptance of the statement. Those governors on hand two hours after the session's scheduled closing unanimously elected Alexander to succeed Kansas Gov. John Carlin (D).

Andrew H. Card, special assistant to the president for intergovernmental relations, said his boss, Mitchell E. Daniels Jr., read the letter before it was mailed to 120,000 prospective contributors and that the office of White House political director Edward Rollins was "very much involved."

The letter said that after "our administration cut your federal taxes by 25 percent, many Democratic governors turned right around and increased state sales and income taxes, wiping out the tax cut given to you by our administration."

In response, the Democratic Governors' Association noted that several Republicans -- including Thornburg, Alexander and New Hampshire's John H. Sununu -- are among the governors who have raised taxes.

The response, signed by 23 of the nation's 34 Democratic governors, chided Reagan for failing to balance the federal budget in five years while "every Democratic governor in the country, save one . . . has a balanced budget." It also said states absorbed many of Reagan's federal budget cuts and raised taxes often to implement his initiatives, such as improving education.

Arkansas Gov. Bill Clinton (D) said the letter was the first time GOP governors had attacked Democrats "with statements that were factually inaccurate.

"They have a perfect right to come into our state and try to whip us. But we can't work as a group if the bipartisan process is going to be savaged by the Republicans," he said.

Texas Gov. Mark W. White Jr. (D) called the letter "claptrap," adding, "If it were issued by a corporation, they'd be sued."

Tim Crawford, finance director of the GOP governors' group, said the letter was "fairly innocuous" compared to some for Democrats.