With Ronald Reagan sitting at his side, Virginia Republican senate candidate John W. Warner yesterday sharply qualified his recent endorsement of former President Ford for the 1980 GOP presidential nomination.

After Reagan told reporters at a press conference that he was undisturbed by Warner's backing of Ford, Warner backed away by volunteering:

"I was asked who I would vote for if the election were held today. Since I think inflation is our greatest problem today - and it was only 4.8 percent in President Ford's last year in office and about 8 percent now - I said I would be for Ford right now.

"I didn't commit myself on what I would do in 1980."

Warner startled many of his backers on Sept. 15 by saying in a televised debate that he favored Ford over other potential GOP candidates.

The timing of the Ford endorsement 12 days before Reagan was to campaign for Warner outraged many conservatives in the state who fervently hope the former California governor will be the party's presidential candidate.

"I wanted to tie a rock around my neck and sink out of sight as soon as I heard about it," one Richmond Republican said yesterday at a reception for Warner and Reagan in the Jefferson Hotel here. He winced when told that Warner had just backed away from his earlier statement.

Reagan is immensely popular with the conservative wing of the Virginia GOP and a crowd of about 400 packed a columned reception room in the ornate, Victorian hotel to cheer his arrival. They paid $25 each to greet Reagan, Warner and Virginia Gov. John N. Dalton.

Warner not only has brought Reagan in for help in his race against Democrat Andrew P. Miller, but will also campaign next month with Ford.

Miller has shunned participation in his campaign by President Carter, who failed to carry Virginia in 1976, but is bringing a parade of generally conservative U.S. senators into the state to help in his race. Miller lunched yesterday with Sen. Henry M. Jackson (D-Wash.) in Northern Virginia.

At the press conference before the reception, Reagan handled questions about the Ford endorsement with aplomb. Asked if he was upset by it, Reagan said:

"No, not at all. When I began this two-month tour of campaigning for Republicans throughout the country, the first candidate I appeared with was in the Ford camp."

He added later: "Of course, everyone would like to have 100 percent support, but too much time is being spent worrying about 1980. These 1978 elections are very important. We have to even up the balance in Congress in this election to preserve our system of checks and balances."

The reception attracted Republicans from throughout the state and not everyone was concerned by Warner's backing of Ford.

"I think he was just trying to be straightforward," Fairfax County GOP vice chairman Thomas M. Davis said. Noting that Warner is making his first political race, he added: "I think he's just not attuned to some of these things yet."

Kenneth D. Smith, Warner's Richmond coordinator who headed the Reagan campaign in the city before the 1976 GOP convention, said. "It was something people worried about until they read about it. It was clear that he didn't volunteer the endorsement, he was pressed to give a name."